A hallmark of the Back to the Future trilogy and a contributor to its popularity is its use of commonalities: running gags, similar events, catch phrases, and parallel situations that recur in the different time frames from film to film. Note that, due to simultaneous productions of Part II and Part III, they have the most commonalities. The following is a list of these, sorted by the movies in which they occur.
Recurring gags throughout the trilogy
- In Part I, in Lou's Cafe of 1955, Biff Tannen says to George McFly: "Hey, McFly, I thought I told you never to come in here." In Part II, that same space is occupied by Cafe 80's of 2015, where Biff's grandson Griff says to Marty Jr. (having previously seen him walking in after mistaking his time-traveling father for him inside): "Hey, McFly, I thought I told you to stay in here!" And in Part III, that same space is occupied by the Palace Saloon, where Biff's ancestor Buford Tannen says to Marty (mistaking him for Marty's great-great-grandfather Seamus McFly before he realised that he wasn't): "Hey, McFly, I thought I done told you never to come in here."
- All three movies have a family meal scene with Marty (One in 1985 with Marty with his parents and his siblings. One in 1955 with Marty, his mother, and his grandparents. One in 2015 with the Marty from that time with his parents and his children and one in 1885 with his great-great-grandparents).
- In all three parts Marty enters the corner saloon/cafe and orders a drink (coffee/Pepsi/whisky) that he never manages to actually drink.
- In Part I there is a car dealership in 1985 Hill Valley named Statler Toyota. In 1955, the same store front is occupied by a Statler Studebaker dealership. In Part II, the 2015 store is the Pontiac dealership (which may or may not be owned by the Statlers) that sells hover conversions, and in Part III, a horse and buggy business named "Honest Joe Statler" is visible as Marty walks into town, though it's not on the same spot.
- In Parts I and II Biff crashes his car into a manure truck. In Part III, Buford collapses into a manure cart. Both of them say "I hate manure" on one occasion. In 1955, the manure truck displays the name D. Jones. In 1885, the manure cart displays the name A. Jones.
- The phrase "back to the future" is used at least once in all three movies. The phrase also gets used in the closing scene of all three movies. In Part I the line is used when Doc comes back from 2015 and tells Marty to come back with him. In Part II, time-stranded Marty rushes up to the 1955 Doc, who doesn't believe what he sees claiming he just sent Marty back to the future to which Marty replies, "Oh, I know you did, Doc, but I'm back. I'm back from the future." In Part III, Doc returns to 1985 with the new time-train and introduces Marty to his new family. Just before Doc leaves, Marty asks him, "Doc, where are you going now? Back to the future?" Doc replies, "Nope. Already been there."
- Towards the end of all three movies, Marty mourns that he'll never see Doc again, only to discover that he's back.
- All three movies involve a chase scene early on in the movie through downtown Hill Valley. In Part I and Part II, these scenes involve variations of a skateboard, which Marty uses to escape. In Part II and Part III, Marty is pulled around Courthouse Square by a rope (in 2015, he chose to hang on to a rope in the back of a jeep; in 1885, he had no choice after being lassoed). In Part III, Marty has no such transportation aid and finally loses a chase, being captured by Mad Dog Tannen's gang.
- Just before the chases in Part I and Part II, Marty shouts out "Hey! Stop!" so that he can borrow a toy to escape from Biff or Griff. In Part I, he detaches a boy's scooter toy to turn it into a skateboard, which he then returns; in Part II, he borrows a girl's hoverboard, which he returns, although the girl keeps Griff's "pitbull" hoverboard instead. In Part III, this is reversed when a boy says "Hey! Mr Eastwood!" and gives Marty back his gun holster, which he then throws to Seamus.
- All three movies have a scene where a slightly bewildered Marty walks through Hill Valley observing the inhabitants and variations of that current time. The inhabitants are also slightly bewildered by Marty's odd appearance. Additionally, during this bewilderment in all three movies he is almost hit by a vehicle.
- In each movie, Marty is knocked out and wakes up at the home of a relative. In Part I, it is his teenage mother in 1955. In Part II, it's his mother in an alternate timeline, 1985A, and in Part III, it's his great-great grandmother in 1885. Each time, Marty wakes up groggily after several hours, thinking the previous events were only a dream. Each time he is reassured that he is safe and sound by Lea Thompson's character, "in good old 1955", "on the good old 27th floor", or "at the McFly Farm". Each time, the location shocks Marty to full awareness. In Parts I and II, Marty exclaims "Mom! You look so..." and then some attribute of his mother he is not used to (as in 1985A, "Mom! You look so... big!" in reference to her breast implants).
- Doc is knocked out in all three films as well, rendered unconscious in three different ways, and hitting his head each time. In Part I, though it is not seen, Doc fell and struck his head on the bathroom sink (and when he came to, he had the inspiration for the flux capacitor). At the end of Part II, Doc fainted upon seeing that Marty had come back from the future. And in Part III, Doc passed out after drinking a shotglass of whiskey, crashing head-first on to a table.
- Michael J. Fox says "Mom, is that you?" five times throughout the Back to the Future trilogy; three times when he wakes up from an injury and twice as Marty McFly Jr.'s sister, Marlene.
- The Hill Valley Clock Tower has some kind of role. In Part I, it is a key component in sending Marty back to the future. In Part II, it is a glass court house in which Marty tricks Griff's gang into running into, as well as the building that gets converted to Biff's Pleasure Paradise in 1985A. In Part III, it has just been built and Marty nearly gets hanged on it by Buford. Marty and Doc also take a picture in front of the not-yet-mounted clock, which Doc later gives to Marty as a souvenir.
- At some point in each of the various time periods, Marty angers the Tannen of the age and usually tries to get out of it with the old gambit of pretending there's something behind him. ("Whoa, Biff, what's that?" while pointing beyond his shoulder.) What's worth noting is that, ultimately, this only works on Biff Tannen specifically: although Biff falls for it in both 1955 and in the alternate 1985 (as do his goons on another occasion), Biff's cyborg grandson Griff, with futuristic sensors around his wrists that automatically raise Griff's arm, and Buford Tannen never gives him a chance (thanks to his trigger finger).
- In each of the three films, when Marty confronts the Tannen of the era in the cafe/saloon, there is a scene where he stands up to them and, due to his small stature, he looks up and over their shoulder as they extend to their full height.
- In all three movies the Tannen of the era pushes a girl or woman to the ground. In Part I, Biff pushes Lorraine down. In II, Biff again pushes Lorraine to the ground in his hotel in 1985A. In III it's Buford pushing Clara.
- In Part I and Part II, Marty pushes Tannen's goons and makes them fall on the ground, and in both cases they collapse in the same domino-like pattern. In Part III, Marty is in danger of getting shot to death, so he runs like hell without toppling anyone along the way.
- All three movies show the famous lightning bolt hitting the clock tower on November 12, 1955, at 10:04 PM. The original version, from Part I is shortened when reshown in Parts II and III and has a new ending - Marty telling Doc he's back from the future. In Part II there are no clips of Marty driving the DeLorean in this sequence; this is presumably to avoid confusing viewers who have just seen him receive Doc's 1885 letter.
- In 1985 and 1955, Mr. Strickland (played by James Tolkan) is the high school's principal. In 1885, Tolkan plays Marshal Strickland, Mr. Strickland's grandfather, however his catchphrase in 1955 and 1985 is "slacker", whereas in 1885, it is "discipline". There was also a deleted scene wherein Marshal Strickland is shot by Buford in clear view of his son and tells him to "remember that word, discipline".
- Throughout the movies, Doc Brown frequently exclaims, "Great Scott!", and Marty frequently says, "This is heavy!" (a colloquialism which the Doc Brown of 1955 never seems to understand). In Part III, a comedic role reversal occurs when at the instant when Marty realizes that he may be the one dying on September 7th instead of Dr. Brown as originally "planned" Marty exclaims, "Great Scott!", to which Doc Brown replies, "I know, this is heavy!"
- The DeLorean had a few modifications done throughout the trilogy. Foremost, its role as a plutonium-powered time machine, activated through engine power at 88 miles per hour. At the end of Part I Doc returns with a hover-converted car, using a "common" fusion reactor to power the flux capacitor. The flying time machine lasted until the end of Part II, when Doc and the car were struck by lightning and sent back to 1885. When Marty and 1955 Doc find the covered DeLorean in a mine during Part III, the tires had rotted over 70 years and microchips had been blown. The flying capability was also disabled due to the lightning strike. Doc utilized 50's era whitewall tires and electronic tube technology to get the DeLorean working again for her last self-propelled trip. The lack of fuel in 1885 brought the last conversion: Flanged wheels were installed so the DeLorean could be pushed by a "supercharged" steam locomotive (the filmmakers used a locomotive from Railtown 1897 for this sequence). At this point, the DeLorean had been retrofitted with technology from all four time periods that it had visited in order to time travel. It was then demolished in a head-on collision with a freight train after Marty successfully arrived in 1985.
- In all three movies, there is either a crash or close call during time travel. Part I has Marty crash into "ol' man Peabody's" barn, then crashes in the "Assembly of Christ" facade. In Part II, Doc travels into cross-hover traffic, then into a jet's flight path. At the end of the film, he ends up being unintentionally sent to 1885 due to the lightning strike. Part III involves Marty encountering Indians (real ones) and ends up with the DeLorean getting shot by an arrow, creating the conflict for the film. At the end of the film, the last DeLorean time travel trip of the trilogy ends with the car getting demolished by a freight train.
- At the end of Part I Doc seems to have been shot but reveals that he wore a bulletproof vest. In 1985A, Biff watches A Fistful of Dollars. Marty walks in on the scene where Clint Eastwood uses a piece of metal as a bullet-proof vest during a duel. In 1885, Marty, going by the name Clint Eastwood, uses that same trick to survive a duel with Buford. It is also noticeable that when Marty gets hanged by the Buford gang, Doc Brown cuts the rope at the critical moment with a shot from his sniper rifle, a clear allusion to the same action performed regularly by the character played by Clint Eastwood in The Good, The Bad and The Ugly.
- Volunteers from the Hill Valley Historical Society looking for donations to save the Clock Tower are seen in Part I 1985 and Part II 2015, while in Part III in 1885, a banner advertises that proceeds from the Hill Valley Festival go to Clock Tower construction.
- At the end of Part I and the beginning of Part II, Doc tells Marty that "you gotta come back with me". Marty asks where, and Doc says, "back to the future". Towards the ends of Part III, there's a reversal of roles between Marty and Doc, as they repeat that similar exchange.
- Aircraft can be heard flying overhead each time Marty returns to the year 1985 from another year. In Part I, it's a helicopter, which flies over the courthouse at the moment that Marty returns from 1955. In Part II, it's a jet which nearly collides with the hovering DeLorean as Marty (along with Doc, Jennifer and Einstein) return from 2015 to the alternate 1985A. In Part III as Marty returns from 1885, a helicopter can be heard overhead as the DeLorean slides down the railroad track.
- In all three films, guns are fired at Marty. In Part I, the Libyan terrorist prepares to execute Marty, but his AK-47 jams; more shots are fired during the chase that follows in 1985. After landing in 1955, "Ol' Man Peabody" also attempt to shoot him. In Part II, Biff shoots at Marty several times with a pistol in 1985A. In Part III, Buford prepares to kill Marty after the spittoon drenches him, but the gun is out of bullets. Marty finally does take a bullet to the chest in the shootout, but is unhurt because he has shielded his chest with a stove door.
- There has been at least one mention of the name "Joey" in all three films. Twice in Part I as Uncle Joey, once in Part II when Biff is speaking with Skinhead, referring to him as Joey, and twice in Part III as the assistant to Chester.
- In all three films, the ending has the DeLorean either leaving or absent. In Part I, the DeLorean shows is capability of flight and disappears into 2015. In Part II, Doc is struck by lightning in the DeLorean, sending it to 1885. In Part III, the DeLorean has been destroyed by a train. Also, Part I and III end with a time traveling vehicle flies to the camera and the credits begin.
- In both Part I and Part II Biff remarks "Well lookee what we have here!" when seeing Lorraine. In Part III Buford says the same phrase when seeing Clara.
Within Part I
- In 1985, Biff tells George, "Hello? Hello? Anybody home? Huh? Think, McFly. Think! I gotta have time to get 'em retyped. Do you realize what would happen if I hand in my reports in your handwriting? I'll get fired. You wouldn't want that to happen, would ya?… Would ya?" In 1955, Biff tells George, "Hello? Hello? Anybody home? Hey, think, McFly. Think. I gotta have time to recopy it. Do you realize what would happen if I hand in my homework in your handwriting? I'll get kicked out of school. You wouldn't want that to happen, would ya?… Would ya?" In both cases, George then promises to work on it all night and "run 'em on over" to Biff in the morning, to which Biff replies "Not too early, I sleep in…" followed by "Oh, McFly, your shoe's untied—" where he slapped him upside on his head. Afterwards, he would say "Don't be so gullible, McFly!". After both conversations between Biff and George, Biff immediately turns to Marty and asks him "What are you looking at Butthead?"
- In 1985, Marty is scared of sending his audition tape to record companies saying "What if they didn't like it? What if they say I was no good?" In 1955, when Marty asks to read some of George's stories, George refuses, giving exactly the same excuse - as well as when Marty urges him to ask Lorraine out, even repeating the "I don't know if I could take that kind of rejection" line.
- 1985's Mayor Goldie Wilson uses the same mayoral campaigning tactics as does Mayor Red Thomas of 1955, involving a megaphoned van and many of the same slogans.
- Marty's uncle "Jailbird" Joey Baines is also found behind bars (of a playpen) as his nephew meets him in 1955 ("Better get used to these bars, kid..."). Joey is also wearing a striped shirt, which is often associated in popular culture with those in jail.
- The same episode of The Honeymooners plays on TV in both eras ("The Man From Space").
- Each time Marty checks his watch (when Doc rings Marty after the opening credit sequence and tells him his clocks are all exactly 25 minutes slow, when 1985 Doc states the time while Marty is filming him at Twin Pines Mall at the beginning of the film, when 1955 Doc and Marty synchronize watches, when Dave reminds Marty of the time at the end of the film, etc.), he gives it a slight double-take and shakes his wrist as if the watch is not working. This is amusing because it is such a slight and subtle recurring gag, and the idea that the world's first human - and most active - time traveler (at that point) doesn't even have a working timepiece is quite ironic.
- In 1985, when Doc tells Marty that the DeLorean requires Plutonium, Marty tells Doc, "You can't just go into a store to by Plutonium." In 1955, when Marty tells Doc that they need a little Plutonium, Doc says, "I'm sure that in 1985, plutonium is available at every corner drug store."
- Throughout the movie the DeLorean engine keeps stalling when Marty tries to get it going (this doesn't seem to happen in the other movies, though it was out of fuel in Part 3, after the fuel tank was pierced). First after he drives away from Old Man Peabody farm, second when he's is trying to drive towards the wire hung to capture the bolt and lightening and third when he arrives back in 1985.
- Towards the beginning of the movie, Linda says (to Marty): "I'm not your answering service, while you were outside pouting over the car, Jennifer Parker called you twice" towards the end of the movie Dave says something similar to Linda about one of her boyfriends, even repeating the line "I'm not your answering service".
In Part I and Part II
- Marty buys a soft drink in downtown Hill Valley and has difficulty opening it the first time (at the Texaco gas station in 1955) because it is in an old-fashioned glass bottle, and the second time (at the Cafe 80's in 2015) because it is in a futuristic container.
- Biff hits George on the head while saying "Hello? Hello? Anybody home? Huh?" in Part I, in 1985 and 1955. In Part II, an older Biff does the same to Marty (thinking he's Marty Jr.) in 2015 (albeit with his cane, and not his fist. Ironically his cane is a fist).
- In Part I, Marty says "he's a peeping Tom", when he notices his father-to-be spying on Lorraine. In Part II, Marty says, "he's a complete wimp", after Spike pushes his future son onto the counter. In both instances, the tone of voice and facial expressions used are identical.
- In Part I, when Marty returns home to see that Biff crashed the family car, Biff tells Marty "Say 'Hi' to your mom for me." In Part II when Marty meets the elderly Biff in the '80s Cafe, Biff says "Say 'Hi' to your grandma for me", thinking that Marty is actually Marty Jr.
- In Part I, Marty checks the newspaper that someone threw in the trash can to check the date shortly after arriving in 1955. In Part II, Marty checks the newspaper that's on Mr. Strickland's porch to check the date shortly after arriving in 1985A. He also refuses to believe the dates in the newspaper are the present. In Part I, he says, "This has gotta be a dream." In Part II, he says, "It can't be."
- In both Parts I and II, Doc says, "Damn! Where is that kid?" In Part I, 1955 Doc says it when he's waiting to send Marty back home. In Part II, Doc says it after he arrived at the Tannens' home to rescue Marty.
- In Part I, Marty drives into a family's barn as soon as he travels to 1955. In Part II, Marty walks in another family's home (which is his home in the normal 1985) in 1985A. In both instances, the father defends his family by threatening Marty's life, while his children encourage him. Those are the only two families shown in the trilogy that are not related to Marty, besides Doc's family at the end of the trilogy.
- When Marty returns to 1985 in Part I, crashing the DeLorean into the Assembly of Christ, Red, the homeless drunk on a park bench, comments, "Crazy drunk drivers". Red is still a homeless drunk in 1985A, Marty bumps into him while exploring 1985A, and Red tells him "Watch where you're going. Crazy drunk pedestrian."
- In Part I, when Marty enters Hill Valley in 1955, one of the first signs he passes is for a showing of the Cattle Queen of Montana starring Barbara Stanwyck and Ronald Reagan. Later, Doc doesn't believe Marty when he tells him Reagan is president, but comes around when he sees the "portable TV studio" (i.e. video camera). In Part II, in 2015, the Café '80s video-waiter is a Max Headroom-style simulacra of Reagan, and the memorabilia in the restaurant include a Reagan mask and a picture of Reagan. Finally, on the front page of the paper Doc checks in the DeLorean to see the timeline being restored, the news item "Nixon to Seek Fifth Term" gets replaced with "Reagan to Seek Second Term".
- In 1955, Biff chases Marty around the Courthouse square, and Marty escapes on a skateboard. In 2015, Griff chases Marty around the Courthouse square, and Marty again escapes, this time on a hoverboard. As an older Biff looks on, he comments "there's something very familiar about all this..."
- Mayor Goldie Wilson's grandson is seen in an advertisement for hovercar upgrades.
- In the end of Part I, Biff tries to weasel out of putting a second coat of wax on the McFlys' BMW. In Part II 2015, Griff berates Biff for not putting a second coat of wax on his car.
- In Part I 1955 Biff tells Marty to "Make like a tree and get outta here." In Part II he uses the same phrase again and is berated by Old Biff (his future self) for getting it wrong.
- In Part I, the DeLorean, in a planned scheme, uses a lightning bolt to activate the time circuits (Marty goes back to 1985) but in Part II, a bolt hits the car and disappears, accidentally sending Doc way back to 1885. Both bolts come from the same storm in 1955.
- In Part I, Marvin Berry, leader of the band The Starlighters, who play the Enchantment Under The Sea dance, places a phone call to his cousin, "Chuck", telling Chuck that he thought this might be "that new sound you were looking for". The song Marty was singing at the time was one of Chuck Berry's hits, "Johnny B. Goode", although Marvin only held up the phone after Marty had already finished singing all the verses and started his guitar solo. Part II shows Marvin getting the inspiration to make that call.
- At the beginning of Part I, Lorraine McFly is verbally negative about her children's activities but states, as Lorraine Baines in 1955 (Part II), that she would be open to her future offspring's decisions, prompting Marty (and his future counterpart, eavesdropping on the same conversation) to mutter he would want that in writing.
- In Part I, Lorraine in 1955 is tending to Marty, when her mother calls to her. Her response is, "Oh my God, it's my mother." In Part II, Lorraine in 1985A is tending to Marty, when Biff calls to her. Her response is, "Oh my God, it's your father."
- Both Doc and Marty waste time unnecessarily by changing clothes. In Part I, Marty does not arrive at Courthouse Square until ten minutes before 10:04 because he changed out of "that zoot suit" into his 1985 clothes. In Part II, Doc changes out of his 2015 style clothing (yellow coat, red shirt and clear tie), and returns wearing another outfit more appropriate to 1985, and the Hill Valley Police pick up Jennifer before Marty and Doc can reach her. By Part III, Marty and Doc have decided that they can return to 1985 without changing out of their 1885 clothing.
- In Part I, Marty comments that he thinks that his mom Lorraine ended up with his Dad because "I guess she felt sorry for him cause her dad hit him with the car". In Part II, Lorraine recounts her son Marty's car accident, and comments that "I think the real reason your mother married him was because she felt sorry for him." Marty alters the outcome of both incidents, without realizing what he's doing.
- In Part I, 1955 Biff grabs Lorraine and she says "Get your meat-hooks off me". In Part II 1955 Biff again grabs Lorraine and she says "Get you cooties off me" in a similar tone of voice.
- In Part I, Marty trips Biff at Lou's Cafe in 1955. In Part II, Griff tries to hit Marty with a bat at the Cafe 80's in 2015, but instead smashes and destroys one of the TV waiters. In both instances, the bullies stand up very tall before Marty and threaten, "All right, punk!" with Marty tricking them both into looking behind them to see a non-existent object. In Part I, Marty successfully punches Biff, but in Part II, tries and fails to do the same to Griff, as he grabs his hand. Afterwards, in both instances, Marty knocks their gangs down and runs out of the cafe.
- In Parts I and II, Doc takes Marty home in the DeLorean late at night. In Part I, Marty sneaks into his bedroom by going through the gate. He tries to do it again in Part II, but the gate has a lock on it so he climbs over the fence.
- Two letters were written in Parts I and Part II. One letter Marty wrote to Doc in Part I was torn up but put back together. After witnessing the events of October 26, 1985 the second, Marty believed that he had failed and that Doc was killed. However, upon Doc coming to consciousness (and revealing the bulletproof vest and taped up letter), Marty found that he was successful. In Part II, after Doc and the DeLorean were struck by lightning into the year 1885, Marty thought he was gone and therefore probably dead again. Afterwards, he received a letter that indicated that Doc was actually still alive.
In Part I and Part III
- The opening scene of Part I includes a photo of silent film comedian Harold Lloyd (no relation to Christopher Lloyd) hanging from a clock tower by holding onto the hands. When Doc is trying to reconnect the electrical cable, Doc hangs from the clock tower by the hands when the ledge breaks beneath his feet. In Part III, Marty hangs from the clock tower when Buford tries to hang him.
- In Part I, Marty and 1955 Doc are present when the bolt of lightning strikes the town clock. In Part III, Marty and Doc have their picture taken with the clock when it's first unveiled.
- In Part I, 1955 Biff calls George an "Irish bug". In Part III, we learn his George's ancestors were indeed Irish. (Although it's true that the prefix "Mc" is more often associated with "Scotch-Irish" clan names, and "O'" more with Ireland itself, the "Mc" prefix is used in Ireland as well, as with its current president, Mary McAleese)
- Marty uses the name of someone famous in his time, but not yet known in the time he's visiting, instead of his own. In Part I (1955), his mother mistakes the name Calvin Klein on his underwear for his and later when he scares his father he calls himself Darth Vader from the planet Vulcan. In Part III (1885), he claims to be named Clint Eastwood.
- In Part I, Marty tells 1955 Doc, "I'm from the future. I came here in a time machine, that you invented..." In Part III, 1985 Doc tells Clara, "I'm from the future. I came here in a time machine, that I invented..." Marty and Doc then tell 1955 Doc and Clara, respectively, that he has to get "back to the year 1985". These expressions also verify the main idea of what Marty and 1985 Doc would have trouble getting through to 1955 Doc and Clara. As 1955 Doc tries to read Marty's mind with the brain-wave analyzer, he cannot tell for what reason Marty has shown up. After 1985 Doc lies to Clara about his connections with the writings of Jules Verne, the similar expression to what Marty said to 1955 Doc indicates the truth about 1985 Doc.
- In Parts I and III, Marty has trouble explaining where he is from to Doc, who both times calls him "future boy" and promptly slams a door in his face (in Part I, the front door of his garage; in Part III, the bathroom door in his mansion). In Part I, Marty proves his origin by explaining how Doc thought up the flux capacitor; in Part III, he proves it by showing Doc's his older self's letter from 1885. Additionally in Part III, Doc tries and fails to explain that he is "from the future" to Clara, who also slams the front door in his face.
- In Parts I and III, Marty talks to his relative as a baby. In Part I, he says, "So you're my Uncle Joey..." In Part III, he says, "So you're my great-grandfather..."
- Marty's 80s catch phrases are quite confusing to the inhabitants of other time periods. In 1955, Marty uses "heavy" twice. Once Doc comments that weight has nothing to do with it, and the second time he gets confused by Marty's repeated use of it and asks if there's something wrong with the Earth's gravitational pull in 1985. In 1885, when Marty picks up a pie plate and sees the word "frisbee" in it, he exclaims "far out!", and Seamus and Maggie McFly comment that it wasn't far at all, but in fact "right in front of him". Also, when Marty tells Tannen "Hey, lighten up, jerk!", Buford looks at his cronies for clarification, and they shake their heads, mystified. Tannen is vaguely able to discern that the expression constituted "mighty strong words."
- In Parts I and III, Doc builds an exquisite model to demonstrate to Marty how the time travel will be done. In Part I, Doc shows how the speeding DeLorean will intersect to capture the lightning bolt. In Part III, in 1885, Doc shows how the speeding locomotive will push the unfueled DeLorean up to 88 mph as it reaches the incomplete bridge. In Part I, Doc apologizes, "Sorry, it's not to scale or painted." In Part III, Doc begins to say "Please excuse the crudity of this model-" and Marty interrupts sarcastically, "Yeah I know, it's not built to scale. It's okay, Doc." Also, while the model car in Part I drove into some boxes and set them on fire (which Doc extinguished quickly), the model train in Part III is caught more safely in a bundle of pillows. In both occasions, after the demonstrations, a woman shows up (Lorraine and Clara respectively).
- Part I finds Doc, the inventor, living in his old garage extension, as his grand home had burnt down in the past. Part III has Doc living in a livery stable, as town blacksmith and scientist.
- In Part I, Marty is about to kiss Jennifer Parker when someone interrupts them for donations for the clock tower, and again when her father honks the horn of his car. At the end of that movie, Marty is about to kiss Jennifer again, but is interrupted by the sonic booms that precede entry of the time machine. Towards the end of Part III, Marty and Jennifer finally kiss on the veranda of her family's house.
- In Part I, after waking up in 1955 ("Mom, is that you?") Marty discovers he is not wearing pants, as they are "over there, on [his mother's] hope chest." In Part III, after waking up on the McFly Farm, as he gets out of his great-great-grandmother's bed, Marty quickly checks to make sure he's still wearing his pants before fully rising out of the bed.
- In Part I, after the DeLorean makes its first trip through time, the license plate (OUTATIME) is shown to be spinning on the ground after the car departs. In Part III, upon the DeLorean's destruction after its final trip through time, the new barcode license plate is shown to be spinning on the ground.
- In Part I 1985, Doc tries to fight off the Libyans with an antique pearl-handled gun, but it fails to fire. In Part III 1955, Doc fires that gun (with the pearl handle painted black) repeatedly to signal Marty to start racing towards 88 MPH.
- In Part I, Doc throws down his pistol, and is shot in the chest by the Libyans. In Part III, Marty deliberately drops his pistol, and is shot in the chest by Buford Tannen.
- In Part I 1985 and 1955, George offers to go over a report with Biff, but Biff tells him "not too early, I sleep in". By opposition, Buford wants to duel Marty at 7 AM, because "I do my killing before breakfast".
- In Part I Doc says, "Where we're going we don't need roads." In Part III 1955 Doc says, "Where you are going there are no roads."
- Early in Part I 1985 Biff complains after having wrecked the McFly's car about the cleaning bill from having spilt beer on his jacket. In Part III Buford is angry after being thrown off his horse and breaking a bottle of "fine Kentucky red-eye". In both instances both Biff and Buford want reimbursement. Similarly, Biff seeks reimbursement from "Calvin Klein" for the $300 damage to his car (mostly in Part II).
- Doc is "supposedly" killed twice, the first time at the beginning of Part I by Libyans (although we don't know for sure if Doc is dead considering that he wasn't moving when Marty looks at him before starting to run from the Libyans). The second is represented by the tombstone (in which he was killed in 1885) in the beginning of Part III by Buford Tannen.
- The scene in Part I where Lorraine comes looking for Marty in Doc's garage, and the scene in Part III where Clara comes looking for Doc in his Livery stable have several similarities. In both cases, Marty and Doc are working on a plan to get back to the future, when the woman unexpectedly arrives. In both, Doc then cries, "quick, cover the time vehicle!" Lorraine and Clara both ask Marty and Doc, respectively, to a social function during their visit. Doc's shocked and bewildered facial expressions are also very similar in both scenes.
- In Part I, the mall was originally called Twin Pines Mall, because Farmer Peabody had raised two pines trees on his farmland. By the end of the movie, the mall carries the name Lone Pine Mall, after Marty ran over one of the pine trees as he was driving away from the farm in 1955. In Part III, the ravine was originally called Shonash Ravine and then later Clayton Ravine, because Clara Clayton originally fell in it in 1885. By the end of the movie, the ravine carries the name Eastwood Ravine (visible on a sign by the track when Marty reaches 1985 after the DeLorean was pushed by the speeding locomotive). One can presume that the ravine is now named after "Clint Eastwood" (Marty McFly) who fell in it with a complete stolen train engine in 1885 and was assumed to have died.
- In Part I, Marty dived into the DeLorean when entering it for the first time. In Part III, Marty dived out of the DeLorean when exiting it for the last time.
- In Part I, Marty tell Lou at the diner that he needs to use the telephone. In Part III, Marty asks Chester at the saloon if there's a back door to the place. In both cases, the answer is, "Yeah, it's in the back." (the latter being rather more obvious)
- In Part I, the people at Lou's Cafe make snide remarks about the clothes Marty's wearing - with Marty's vest being repeatedly referred to as a "life preserver". In Part III, the people at the Palace Saloon also make snide remarks about the clothes Marty's wearing - including Marty's Nike runners being referred to as "moccasins". Interestingly enough, in the fourth draft of the first movie, Marty's Nike runners (with "green swooshes") were the target of derision - and possibly in the scene filmed with Eric Stoltz
- In Part I in 1955, after Marty asks Lou Carruthers for a Pepsi Free, Lou says, "You want a Pepsi, pal, you're going to pay for it!" In Part III in 1885, after Marty asks the bartender for ice water, the bartender says, "You want water, you better go dunk your head in the horse trough out there. In here, we pour whiskey."
- At the beginning of Part I, the camera pans over the clocks, and then Doc's automatic machine. In Part III, the camera pans over over the cuckoo clock, and then Doc's meal making machine .
- In Part I Doc is frustrated because Marty is nowhere to be found as the 10:04 pm deadline for going back to the future approaches. Marty's excuse, for showing up with only ten minutes to spare, is that he didn't want to go home in uncomfortable clothes ("that zoot suit"). In Part III, Marty is frustrated because Doc is nowhere to be found as their planned deadline for going back to the future approaches. When he finds Doc, with only ten minutes to spare before the 8:00 am gunfight, Doc's excuse is that he's been sitting in a saloon all night.
- In Part I, Doc explains to Marty that he came up with the idea for time travel after falling off a toilet, as he was trying to hang a clock over it. In Part III, the camera gives us a brief glimpse of the clock over the toilet, after a frightened Doc ran into the bathroom.
- In Part I, when Stella introduces her family, she points out that Marty already knows Lorraine. At the end of Part III, when Doc introduces his family, he points out that Marty already knows Clara. Lorraine was the lead female character in Part I, while Clara was the lead female character in Part III.
- Both Stella Baines (in 1955 in Part I) and Maggie McFly (in 1885 in Part III) have the same description for Marty when he visits for dinner --- He's "a strange young man"
- In Part I, Marty asks if the DeLorean time machine runs on gasoline, and Doc replies that it requires a nuclear reaction. In Part III, Marty assumes that Mr. Fusion would run the engine, and Doc replies that the engine runs on gasoline.
- When Marty is preparing to break the time barrier, he is always on the verge of crashing into something at 88 miles per hour. In Part I he races toward a Fox Photo (crashing instead into a scarecrow and the barn at the Peabody farm), and he races toward the Town Theater (which he crashes into in 1985). In Part III, Marty races towards a wall at another theater (veering instead into the path of Indians on horseback) and he races toward the "End of Track" sign at the ravine (safely making it across without crashing the car into anything--- although a train crashes into the car). With the exception of the end of the track, Marty is always aiming at something film-related, whether it's the kiosk for a film developer, a cinema, or a drive-in theater. Doc does all the driving in Part II. With a remote control, Doc has the DeLorean racing straight at him and Marty in the first experiment (in Part I), but seems to always allow himself enough room to avoid a possible collision when he's behind the steering wheel.
- In Part I, Marty exclaims, "What the hell is a gigawatt?" In Part III, Marty exclaims, "Who the hell is Clara?"
- In Part I, Marty's uncle Milton in 1955 wonders at his description of the episode The Honeymooners as "a classic", commenting that it is brand new. In Part III, Clara in 1885 laughs at Doc's recounting of reading Jules Verne's Twenty Thousand Leagues Under the Sea when he was a boy, commenting that it had only been published ten years before. They also both have anachronistic errors. It is November 1955 when the episode of The Honeymooners discussed airs. In reality, the episode actually aired on December 31, 1955. Because it is 1885 when Clara says Twenty Thousand Leagues Under the Sea was published ten years before, she is saying that that happened in the year 1875, but the book was actually published in 1870. (In fairness to Clara, the first English translation of Vingt mille lieues sous les mers had come out slightly more than ten years before 1885, in 1873)
- At the end of Part I, the DeLorean lifts off the road, flies away from the viewer, before turning around and flying into the viewer as the credits begin. At the end of Part III, the Time Train takes off and makes the same flight into the viewer, prompting the credits to begin.
- In Part I, Marty drives into Old Man Peabody barn and he hears a sound of an animal, (in this case a cow which there are a few of) in Part III he drives into a cave and hears a simliar noise (from a bear this time).
- In Parts I and III, train whistles can be heard blowing in the distance. In Part I, as Marty skateboards to Twin Pines Mall, a train in the distance blows its whistle. In Part III, the train that Marty and Doc eventually use to push the DeLorean up to 88 MPH can be heard blowing its whistle numerous times. The train whistle blow in Part I was unscripted.
- In Part I, there is no plutonium left in the time machine, and the only source that can help Marty return to 1985 is a bolt of lightning. In Part III, Marty rips the fuel line of the time machine, and all the gas leaks out, so Doc and Marty have to find a way to push the time machine to 88 mph in order for Marty to return to 1985 again.
In Part II and Part III
Because Part II and Part III were written and filmed together, it was easier to introduce new commonalities and themes, and do their best to relate them back to Part I.
- Marty McFly is called "chicken" in Part II by both Griff and Needles in 2015 and Biff in 1955, and replies with "Nobody calls me chicken!" He's called "Yella" (yellow) by Buford in Part III and replies the same way with the same dramatic music cue. It should be noted that Needles calls Marty "chicken" at the end of that film without the traditional reaction and cue because Marty has learned that allowing himself to be provoked can lead to disaster.
- In Part II, Marty Jr laughs at his own joke, after asking if Lorraine can "just shove [the pizza] in [his] mouth". In Part III, Seamus laughs at his own joke, after commenting that he "never heard any complaints from the pigs". Dave later on laughs at his own joke, after asking Marty if he's supposed to be Clint Eastwood.
- In Part II, after 1985-Jennifer and 2015-Jennifer pass out, Doc is saddened because after he thinks he'll destroy the time machine, he'll "never get a chance to visit my favorite era: The Old West. Better to devote myself to that other great mystery of the universe: women." Later, the DeLorean gets struck by lightning and Doc actually winds up in his favorite era and, ironically, encounters "that other great mystery of the universe", Clara Clayton.
- Marty shows off his expert shooting skills. In Part II it's in the '80s Cafe on the Wild Gunman arcade game, and in Part III it's at a demonstration booth for the Colt Peacemaker. In Part II, one of the 2015 boys declares that the Wild Gunman is "like a baby's toy", while in Part III, the Colt Peacemaker salesman tells Marty that his gun is so easy even a baby could use it, then taunts him with, "Surely you're not afraid of something a baby can do?"
- Parts II and III have Marty throwing something with a Frisbee technique at a Tannen. In Part II it was a tray at Biff when he was Marty's step father. In Part III it occurred at the party when Mad Dog was going to shoot Doc and Marty uses an empty pie pan from "The Frisbie Pie Company".
- In Part II, in 1985A, Marty finds his father's grave in Oak Park Cemetery. In Part III, in 1955, Marty finds Doc's grave in Boot Hill Cemetery.
- In Part II 1955, Mr. Strickland's office door has the word "discipline" written under his name. In 1885, Marshall Strickland tells his son to "Remember that word: 'discipline.'"
- In Part II 2015, Lorraine and Marlene are heard talking about how, 30 years ago, Marty tried to prove he wasn't chicken and ended up in an automobile accident with a Rolls-Royce. That single event ruined his life — the driver pressed charges, and Marty broke his hand, forcing him to abandon his dream of a music career. In Part III 1885, Doc warns Marty not to lose his judgment every time somebody calls him a name, as "that's exactly what gets you into that accident in the future." Finally, in Part III 1985, Needles calls Marty a chicken to push him into street racing. Marty keeps his cool and doesn't race Needles, then looks on to see that, had he raced, he would have hit a Rolls-Royce.
- In Part II, after Marty expresses in Doc's lab in 1985A how he wished he never bought the sports almanac in 2015, Doc tells him that it's "all in the past". After Marty points out that Doc means "the future", Doc responds with frustration. In Part III, a similar scene plays out just before Marty heads back to 1885, when Doc says that he'll "see [Marty] in the future". This time, after Marty points out that Doc means "the past", Doc cheerfully agrees that Marty is right.
- The phrase's, "Hey the big "M"and "How's it hangin' McFly," are said by Needles to Marty in both 2015 and 1985. In both cases Needles calls Marty a chicken.
- Throughout Part II and III, Doc is constantly talking about destroying the time machine and finally at the end of Part III is destroyed (by a freight train)
- In Part's II and III Marty gets mistaken for one of his family (by the Tannen of the era) first in 2015 he's mistaken for his future son first by Biff then by Griff and his gang (although he was supposed to be taking his place anyway) In 1885 he's gets mistaken for his great-great-grandfather by Buford.
- Marty is unaware of relatives he has had. In Part II, he questions having a daughter. In Part III, he finds out and does not seem to believe that his great-great-grandfather Seamus had a brother named Martin McFly.
Within Part II
- Doc and Marty leave an unconscious Jennifer in an alley in 2015 and walk away. Later, in 1985A, they leave an unconscious Jennifer in a porch swing in front of her home, and drive away. Although Marty has misgivings on both occasions, he lets Doc talk him into leaving his girlfriend behind both times.
- Biff Tannen is surprised to see a flying DeLorean, and it happens in four different eras. In 1985, he comes out of the McFly home to show Marty his new matchbooks, and witnesses the DeLorean rise from the ground and disappear in a flash. In 2015, Biff, now 78 years old, comes out of Cafe 80's just as Doc lowers the car to the street. A flying car is no surprise to him, but "A flying DeLorean? I haven't seen one of those in 30 years." In 1985A, he's on the roof of his hotel, checking to see if Marty has indeed plunged to his death, and is surprised when Marty is standing on the hood of a flying car; and even more surprised when Doc opens the gull-wing door and knocks him out. Finally, in 1955, Biff is surprised as he watches Marty fly away on a rope hanging from the DeLorean. Distracted, he crashes into a manure truck for the second time that week.
- The dangers of trying to "get rich quick" are a recurring theme in the second film. Marty Jr. (of 2015), Marty Sr. (of 1985 and 2015), and Biff (of 1955 and 2015) are each presented with a financial opportunity, and in each case, taking a chance ends with disaster. Marty Jr. had been coerced by Griff to commit a robbery, got caught, and been sentenced to 15 years imprisonment (though this is altered when Marty of 1985 says no when Griff asks him his decision "about tonight's opportunity"). Before returning to 1985, Marty sees the potential of taking Grays Sports Almanac back with him for "making a few bucks on the side", and ends up regretting the purchase. Marty Sr. of 2015, a 47 year old man, is talked by Needles into taking a risk on an illegal endeavor that "could solve all your financial problems", and ends up getting fired instead. "Old Biff" (of 2015) takes advantage of a chance to enrich himself by going back to 1955 and giving his younger self the almanac; though Biff of 1985A is fabulously wealthy, old Biff collapses upon his return to 2015, having endangered his own existence. Young Biff accepts the almanac in 1955, and his fate is altered as he wrecks his car a second time and loses the almanac again.
- All of the time travelers (except for Einstein the dog) have an encounter with themselves in another era. Jennifer Parker from 1985 meets face to face with Jennifer McFly in 2015, and both faint. "Old" Biff, who is 78 years old, spends a day in 1955 with 18 year old Biff, during which he gives him Grays Sports Almanac. Doc from 1985, while warning Marty not to run into his "other self", accidentally catches the attention of Doc from 1955, who is installing the electrical cables for Marty's trip home, and hands him a wrench. This does not cause a paradox, but rather a pair o' Docs. In the oddest encounter of all, Marty from Part II is knocked out cold when Marty from Part I leaves the Enchantment Under the Sea dance and opens the door just a little bit too forcefully. There are no such encounters in the first or third film, although Part III has one actor, Michael J. Fox, appear onscreen as both Marty and Seamus McFly in the same scene numerous times.
- In 2015 Doc is worried that Jennifer could encounter her future self, and that "the encounter could create a time paradox" that would "unravel the very fabric of the space time continuum and destroy the entire universe", later Marty says that Biff's guys are going to jump his other self, and Doc says that if Marty's "other self" missed the lightening bolt at the clocktower, he won't get back to the future, and they would have a "major paradox" (to which Marty replies "wait wait a paradox, you mean one of those things that can destroy the universe") both times Doc says "Great Scott". there were also other worries of simliar situations "you must let old Biff think he's succeeded so he'll leave 1955 and bring the DeLorean back to the future" and when Doc talks about both he and Marty avoiding there "other selves".
- In 1985A Biff is married to Lorraine, also a video (played in the museum) says that Biff made a million betting on a horse race in 1955, and it also showed the wedding, you can tell Lorraine's not happy with the marriage. In 1955 Biff says that he's "going to marry [Lorraine] someday". Also Lorraine says "I wouldn't be your girl even if you had a million dollars". (although this is earlier in the timeline and what Lorraine says in 1955 tallies with her unhappiness of the marriage)
- In 2015, a newspaper that says Marty Jr. will be getting arrested later says that Griff and his gang are getting arrested after they crash into the courthouse. In 1985A, a newspaper says that George McFly got killed, and another says Doc Brown got committed, but after Marty burns the almanac in 1955, the newspaper with the headline about George McFly says that George is honored, and the newspaper with the headline about Doc Brown's being committed says he is commended.
- Doc says that the single event of Marty Jr getting arrested caused a chain react that completely destroyed Marty's family and later that Jennifer's encounter with her future self could result in a paradox that would cause a chain reaction that could destroy the universe (or the galaxy), later 2015 Lorraine says that an automobile accident caused a chain reaction that destroyed Marty's life (though she didn't actually say "destroy")
Within Part III
- Jules Verne is an ongoing theme in Part III, while the name was never mentioned in Parts I and II. Towards the beginning of the movie, 1955 Doc explains to Marty how he was fond of Jules Verne since he was eleven. Soon after that, they discover that the DeLorean was hidden behind some boards that had Doc's initials engraved in it, which was inspired by Jules Verne's Journey To The Center of the Earth. Later on, as Doc is stargazing with Clara, Clara reveals that she is also a fan of Jules Verne. After Marty returns to 1985, as Doc introduces his family to Marty, and their two sons are named Jules and Verne.
- As 1955 Doc is preparing to send Marty back to 1885, Marty worries that he'll crash into the painting of the Indians. In 1885, as Doc and Marty are looking at a map on how they'll return to 1985, Marty worries about how the bridge won't be completed until 1887. In both cases, Doc chides Marty for "not thinking fourth dimensionally". It's interesting to note that, while Marty doesn't crash into the painting of the Indians, he does crash into some real Indians back in 1885.
- In 1955, Marty finds a photograph of Doc taken next to the unmounted clock at 8:09 PM. Later on, in 1885, Marty and Doc have their picture taken in front of the clock at 8:09 PM. After returning to 1985, Marty notices that the half of the photograph that he was standing on is missing, providing an interesting ambiguity. A few minutes later, as a souvenir, Doc hands him a framed photograph of them standing in front of the clock.
- In 1955, Marty finds a photograph of his ancestors. He points out his great-grandfather William, noting him as a "good looking guy". Later on, he gets to meet his great-grandfather William, as an infant. Michael J. Fox, who plays Marty, also portrayed William McFly in the photograph.
- When Marty asks for ice water, Chester the bartender replies "Water? You want water, you better go dunk your head in the horse trough out there", and was then given a shot glass of whiskey instead. When Doc passes out from one shot of whisky and is awoken by the "wake-up juice", he immediately runs outside and dunks his head in the horse trough.
Back To The Future: This phrase has been used in the trilogy a total of 16 times (19, if you count the ending from Parts I and II repeated at the beginning of Parts II and III.). In Part I, 1955 Doc and 1985 Doc each says it once. In Part II, Marty uses that phrase three times, 1985 Doc says it twice, and 1955 Doc says it once. In Part III, Marty uses that phrase five times, 1955 Doc uses that phrase twice (once when reading the letter from his older self), and 1985 Doc uses that phrase once. Marty also said it once during a Part I deleted scene
Butthead: This expression has been used in the trilogy a total of 11 times. In Part I, 1985 Biff uses the word once while 1955 Biff uses it twice. In Part II, 2015 Biff uses that word three times, once when addressing his younger self in 1955. 1985A Biff uses that expression once. 1955 Biff uses that word three times, twice when protesting his older self's use of that expression. In Part III, 1985 Biff uses that word once, before realizing that it was Marty who approached him.
Great Scott: This expression has been used in the trilogy a total of 15 times (16, if you count the ending of Part II repeated at the beginning of Part III.). In Part I, 1955 Doc says it on three occasions. In Part II, 1985 Doc says it on five occasions, while 1955 Doc says it once. In Part III, 1955 Doc says it on three occasions, while 1985 Doc (now in 1885) says it on two occasions. Finally, Marty uses the expression, in a humorous reversal of roles.
Heavy: This expression has been used in the trilogy a total of eight times. In Part I, Marty says it on two occasions. In Part II, young Marty says it on three occasions, while 2015 Marty says it once. In Part III, Marty only says it once. However, Doc finally uses that expression in a humorous reversal of roles.
Hey, McFly: This expression has been used in the trilogy a total of nine times. In Part I, 1955 Biff says it on three occasions. In Part II, 2015 Biff and Griff both say it on two occasions, while one of Griff's lackeys says it once. In Part III, Buford says it once. It is interesting to note that the expression is not used by 1985 Biff in any of the timelines.
Perfect: Marty uses this sarcastically at various points in all three films, while Doc says this in Part II, as does Marty Jr. when he asks for a Pepsi Perfect in the Cafe 80s.
Slacker: Within Parts I and II, this expression has been used a total of eight times. In Part I, 1985 Strickland and 1955 Strickland each use that word twice. In Part II, 1985A Strickland uses that word twice, which Marty acknowledges that he is. 1955 Strickland uses that word once.
Think, McFly, Think: Within Parts I and II, Biff uses this expression on three occasions. In Part I, 1985 Biff and 1955 Biff each use that expression with George. In Part II, 2015 Biff uses that expression with Marty (thinking that he's Marty Jr.)
You're The Doc, Doc: Within Parts II and III, Marty makes this comment three times. He uses it twice in Part II and once in Part III.
Recurring Gags that Ran Through Deleted Scenes
- In a deleted scene titled, "Got a Permit?," Marty fears that his mother, Lorraine, will call him gay, and Doc asks, "Why shouldn't you be happy?" (This is another confusion with whatever Marty has said.)
Other relevant notes
- A letter read in The Secrets of the Back to the Future Trilogy brings up the subject of history repeating itself in the trilogy, to which Kirk Cameron agrees with. The idea is demonstrated by showing some recurring gags (specifically, Marty entering the Palace Saloon, Lou's Cafe and The Cafe 80s).
- The movie makes use of several oxymorons and contradictions, including in the title itself and in the name of the city, Hill Valley. Likewise, when the time machine travels through time, it always leaves fire trails where its tires would have been; however, when it appears in the destination time, it is "damn cold" according to Doc Brown and frost is visible on the surface of the vehicle. Additionally, the term "flux capacitor" can be seen as an oxymoron.
- Three sonic booms are always heard when the DeLorean appears in the destination time. After each trip, the delay between the three sonic booms becomes larger.
- In a deleted scene from Part II, Marty Jr complains that he can watch two channels on his goggles. 2015 Marty responds by explaining that, when he was Marty Jr's age, if he wanted to watch two channels at once, he had to put two television sets next to each other. This scene bears some similarity to the scene in Part I, where Lorraine asks Marty if he has a television set, and Marty says that he has two of them. Stella insists that Marty is only teasing, as "nobody has two television sets". Also, the beginning of Part III reveals that Doc has two television sets in 1955.
- In a deleted scene from Part II, when Marty runs into Dave in 1985A, Dave asks Marty if he slept in his clothes again. Dave asks the same question to Marty at the end of Part I.
- In Part II, Old Biff steals the time machine and goes back in time to give "'50s Biff" the book. Old Biff then returns to the future to return the machine. However, the Doc says that if they go into the future from the altered past (1985A) it will be the future of 1985A (2015A), not the normal 1985. By this, Old Biff should have arrived in 2015A, when Biff was rich, and not the normal 2015. Bob Gale and Robert Zemeckis explain in the BTTF FAQ that their intention was that Old Biff did return to 2015A, because the original 2015 transformed into 2015A around Marty and Doc as they were carrying Jennifer back to the DeLorean. A deleted scene shows Old Biff vanishing immediately upon arriving back to the future, and it is explained by Gale and Zemeckis that Lorraine must have shot Biff sometime between 1985 and 2015 (the FAQ suggests a date of 1996, while Gale suggests a date of 1991 in the DVD commentary for this deleted scene) after getting tired of their marriage, resulting in old Biff's lack of existence from the future Hill Valley. This explanation, however, might result in a time paradox (how could Old Biff have traveled back if he never existed?). Then again, due to the fuzzy and complex nature of the "ripple effect" in the movies, it might not cause a paradox at all.
- In Part II, when 1985 Jennifer comes face to face with 2015 Jennifer, they both pass out from the shock of seeing their former/future self, however 2015 Biff meets 1955 Biff to give him the book without incident. Zemeckis and Gale also address this issue in the BTTF FAQ, explaining that "Jennifer definitely realizes she is seeing herself 30 years older and that puts her into shock. Young Biff, however, has no idea who old Biff really is -- he thinks it's just 'some old codger with a cane.'"
- There are actually at least three separate "copies" of the DeLorean time machine in existence at the same time on November 12, 1955. One of them is the machine that Marty originally takes back to 1955 in Part I. The second is the one that Biff takes back to 1955 in Part II to give the sports almanac to himself. The third is the DeLorean that Marty and Doc take to 1955 in Part II to stop Biff from giving the almanac to himself. A possible fourth copy of the time machine is the DeLorean that Doc hides in the old mine to send to Marty in Part III, although based on the way the "ripple effect" is shown to work in the movies, this one would probably not have appeared in the mine until after Doc was sent back to 1885 by the lightning strike.
- In several films, Biff Tannen is shown to have no understanding of sayings. For example, in Part II, the 1955 Biff says that his rejection by Lorraine is "as funny as screen doors on a battleship" whereas the correct phrase would be "as funny as a screen door on a submarine." This extends to the Back to the Future ride at Universal Studios where he tries to steal a time machine and trips the guards with marbles saying, "Have a nice trip, see you next winter!" whereas the correct phrase would be "See you next fall!" In parts I and II, he says to someone "now make like a tree and get outta here!", which in Part II, his older self slaps him and corrects him to say it to "make like a tree and leave."
- Biff (young or old) is frequently shown to use the pejorative phrase "Butthead." As seen in the Back to the Future: The Animated Series, his ancestors and descendants also use the term, most notably Beauregard Tannen, a Confederate General in the Civil War, who calls his enemies "buttocks brains" but changes it to "butthead" after being corrected by Verne Brown.
- It is a common misconception that Mayor Red Thomas of 1955 and Red the Bum of 1985 were meant to be the same character. According to Bob Gale's commentary on the Back to the Future DVD set, the name of the bum was ad-libbed by Michael J. Fox. Gale also commented that the photo of the mayor in 1955 on the side of the campaign van was that of set decorator Hal Gausman, whereas the bum was played by George "Buck" Flower.
- Throughout the trilogy (and despite Jennifer's claim that Doc "always" says it), Doc never actually says the quote, "If you put your mind to it, you can accomplish anything," on screen. The line was only used in Part I; twice by Marty and once by George. At the end of the trilogy, though, Doc is heard saying, "Your future is whatever you make it, so make it a good one."
- After Marty arrives in 1885 in Part III, the DeLorean is hit by an arrow which ruptures the fuel line, causing all the gasoline to leak out. Many fans wonder why Marty did not simply siphon the gas from the other version of the car - the one which Doc had buried there (and which Marty unearthed in 1955 and used to travel to 1885). In the BTTF FAQ Gale and Zemeckis suggest two separate answers. Firstly, all the fluids must be drained out of a car before storage for extended periods of time, so Doc would have done so before burying it in the mine. Secondly, Doc would not have dared risk damaging the car in the mine by uncovering it again, since Marty had uncovered it in 1955 and used it to get back to 1885, so any damage to it in 1885 after Marty had already arrived could create a paradox.
- In Part I Michael J. Fox and Lea Thompson are Marty McFly and Lorraine Baines, son and mother, and Marty must avoid her infatuation with him; in Part III, as Seamus McFly and Maggie McFly, they portray a married couple in 1885.
- In Part I, while Marty is playing "Johnny B. Goode" - a girl suggests that George should consider running for class president. This alludes to how Bob Gale came up with the plot for Back to the Future. He was looking through his father's yearbook, and discovered that his father was the president of his graduating class. Gale then thought of how he never really associated with the class president of his own graduating class. Thus, he came up with the idea of a time traveler meeting his parents - from when they were the same age as him.
- In Part III, when Doc is telling Marty that they have to go back to the future to avoid Doc meeting Clara, Marty says, "I tore a hole in the gas tank when I was landing", implying that the Delorean was originally supposed to still be able to fly in Part III. Apparently, this was changed later, but the line is still in the movie. Of course, he could also have been using it as "landing in 1885."