Back To The
Future Part I
The Tower Clock turns 10:01pm twice during the storm.
Marty sets the Delorean to return to 1985 at 1:24am, but when he arrives the clocks on the dashboard and above the shop window say 1:23am instead.
In the cafe George stares at Marty when he suggests Goldie will become Mayor. He then looks at Goldie, who was standing behind him, without turning around.
Marty keeps lowering the camera while he's filming the first time jump. This includes the part where Doc says "This sucker's electrical..." etc. However, when the video is played back in 1955, the picture remains locked on Doc's face throughout the whole sequence.
Einstein's time jump lasts about 70 seconds but the stopwatch is only sixty seconds behind Doc's.
The Delorean is clean when it materialises after Einstein's journey is complete, but when Doc opens the door a moment later the car is packed in ice.
When Doc suggests that they can go back in time to witness the birth of Christ, he keys December 25th, year 0 into the flux capacitor. Three problems. Firstly, the date December 25th was almost certainly not the date of the birth of Christ (no-one knows for sure - it was chosen by the Roman Catholic Church for Christmas Day just to coincide with the old Pagan festival of Yule). Secondly, if Christ existed he was probably not born until about the year 4 AD anyway (absurd, but the established fiction). Finally, and this is the really important one, there was no year 0 - after the year 1 BC came to an end, the year 1 AD began.
Back To The
Future Part II
The ladder above the stage at the school dance wasn't there in the first film.
The shirt Marty was wearing at the beginning of the film disappears after he changes into the futuristic outfit. It should be in the Delorean, but it never surfaces again.
Reality fails to change after Old Biff goes back in time (surely he should have returned to a future where he was ruler of Hill Valley...?).
Doc and Marty leave Jennifer lying on a pile of boxes. When the two policewomen find her she's sat on the ground.
Biff's car doesn't have a rear-view mirror in the Garage, it does on the road.
At the very beginning of the movie, the scene when the Delorean is about to take off for 2015 is re-filmed. There is a Volkswagen van by the side of the road that was a different colour in the first film.
On a similar note, various other scenes from the first movie are out of synch when re-filmed here.
The thunderstorm stops dead after the Delorean gets struck by lightning, but it's still going when the lightning strikes the clock tower.
Marty's cap disappears after he leaves it on top of the video game machine.
When exactly does Marty grab the Almanac after Biff is laid out on the floor? Marty definitely hasn't got the book when he exercises "CPR" (i.e. a right hook), and he clearly doesn't search any of Biff's pockets, yet when the camera cuts back to him he suddenly has the book in his right hand.
Griff's "pit-bull" hover board smashes through the clock-tower window, but the kid on the other side of the lake has it a few seconds later.
Doc says if anyone encounters his future/past self it will cause a paradox that will destroy the Universe, or they will pass out. Later, relative time, Biff from the 1950's encounters his future self from 2015 and nothing happens.
Biff closes up the safe, and swings the portrait back into place over it. As he turns back to Marty, the portrait starts to swing away from the wall again. Then after Biff sits down, the portrait is suddenly flush against the wall once more.
(Look REAL close for this one.) During the scene in the tunnel, we get an extreme close-up of the right rear hubcap of Biff's car. As the wheel starts spinning, the camera crew are reflected in the surface of the hubcap.
When Doc talks to his past self, the '55 incarnation's breath turns to steam in the cold air, but the '85 incarnation's does not.
When Marty is dicing with death hoverboarding on the trunk of Biff's car, the book lands on the windscreen at an angle it couldn't have.
Back To The
Future Part III
The Old Doc in 1885 has no memory of dressing Marty in the silly cowboy outfit, nor of seeing his own gravestone.
The arrow that Marty finds lodged in the side of the Delorean wasn't there when he reversed into the cave.
In any case, the arrow couldn't possibly have been fired into the Delorean at the angle that Marty finds it in - it's lodged into the left side of the car at roughly a ninety degree angle, but when he was fleeing from the Indians, the only parts of the car that faced them square-on were the right side and the rear.
Buford Tannen doesn't look anything like his photo in the Tannen Museum in the second film.
The Delorean comes grinding to a halt on the railway line. Marty never moves it again, but it's suddenly a good ten yards further along the track when it's hit by the train.
If the steam engine is travelling at about 85 miles per hour, it must surely be moving faster than the hover-board's maximum speed. And yet, after Doc catches Clara, the hover-board actually ACCELERATES and appears to overtake the Delorean.
The horse that Doc is riding during the chase to rescue Clara changes from brown to black then back to brown again.
Buford stumbles on his first line of the film ("Hey, McFly! I thought I'd done... er, told you never..." etc).
The buckle on the front of Clara's hat vanishes between scenes.
When the photograph of Marty and Doc is taken, the time on the clock suddenly skips forward thirty seconds.
The hat is undamaged by the bullet that knocked it off of Doc's head.
When the steam engine plunges into the ravine, the explosion does not occur in quite the right place i.e. it's clearly a few yards behind the position where the engine crashes into the ground.
How did Doc know where to find Marty and Jennifer at the end of the film? Surely with his prior knowledge of the accident with the Rolls Royce he would have expected to find them at the Lake, or in a hospital - or even a police station. (He might have time-jumped further into the future first and found out I suppose, but again we have to ask why he would have bothered.)
The appropriate components for building a flux capacitor weren't invented until 1947, according to Doc's letter, but Doc manages to build a flux capacitor and fits it into a steam train before the turn of the 20th century.