Continuity mistake: When McFly gets to the village in 1885, he walks beside the manure guy and the sun changes between shots.
Revealing mistake: At the festival, after Marty is given the gun he encounters Seamus and Maggie. Due to the Vistaglide camera effect where Marty was later added to the scene, she is unable to look at where Marty is supposed to be. This is very noticeable when Seamus says "buffoon" and Marty turns around and starts to walk, but Maggie keeps staring at where he was. Also when the scene ends and she looks at Marty and warns him to watch for the future, she's totally missing the spot.
Continuity mistake: Just when Marty parks inside the cave to hide from the Native Americans, one wearing a war bonnet jumps over the mount. When the angle changes, the man is gone and has been replaced by two riders with no war bonnets.
Continuity mistake: When Marty is about to go to 1885, before Doc shoots his gun, you can see the coils on the face of the DeLorean is brown, later when he is driving toward the screen, the coils are clear silver again.
Continuity mistake: In the saloon, Mad Dog shoots at Marty, forcing him to dance. Marty goes into his moon walk dance, and just before he launches the spit jug at Mad Dog, he does a jump. Watch as he lands - the jug is suddenly 4 to 6 feet to the right of him.
Factual error: When Marty travels back to 1885 and meets the Native Americans, we see a view from inside the car with the digital speedometer. The car is still going over 70 when the Indians are less than 2 metres away from the front of the car. There is no way the car would be able to stop that quickly from that speed.
Character mistake: At the ravine, upon learning that the bridge doesn't exist yet, Marty states to Doc "We can't wait a year and a half for this to be built". If you carefully look at the sign, it says the bridge is opening Summer 1886. That's under a year away, not a year and a half from Sept. 1885.
Factual error: At the end of the movie, when the new time machine built into a steam locomotive begins flying and departing, the train signals are still running and the barrier crossings are still down. The train signals should have stopped once the flying time machine locomotive was off the tracks.
Suggested correction: Train signals generally stop once the end of the train is a good distance away from the road where the signals sit, by sensors. In the film, the train is too close to the road and by lifting up in the air, the sensor to stop the signals were never reached by the train.
Continuity mistake: When Marty is about to race against Needles, he holds the wheel with both hands. An instant cut later, his hands are gone.
Continuity mistake: When Marty walks around the old town and watches the manure guy work, a huge shadow covers the whole place. An instant cut later, it's all sunny, revealing it was shot at a different time of day.
Continuity mistake: When Marty is about to race against needles, the camera zooms in towards his car. Notice a big rectangular black object reflected on the car. From opposite angles it disappears and there's just green fields. The black object was most surely a structure to hide the camera equipment.
Continuity mistake: After Marty gets to 1885, a bunch of Indians are running to him and the cavalry behind them, but in the open view one second before, the cavalry was not there.
Continuity mistake: In 1955 while the Doc is recording some stuff, while Marty behind him is sleeping on the couch, his head moves from side to side between shots.
Continuity mistake: While Marty is outside the mine, the sun changes on the floor.
Continuity mistake: While Doc saves Marty from Biff the sun changes between shots.
Revealing mistake: When Doc jumps from the horse to the train, right after he hurries Marty, the man on the horse is an obvious stunt double for Michael J. Fox.
Continuity mistake: When Marty holds the temperature-meter and warns Doc to put the yellow log inside the firebox, his finger suddenly disappears between shots.
Continuity mistake: When Buford hangs Marty, he puts the rope around his neck once. In the close-up the rope goes around twice.
Continuity mistake: When Marty and Buford duel, Seamus' distance to the bartender keeps increasing / decreasing randomly between shots.
