Continuity mistake: When Doc's about to send Marty back to 1885 from 1955, and Marty's dressed up...when Doc's walking back and forth loading up the car - look at the shadow from the building. You see it changes by several feet in a few seconds as the scene was obviously shot throughout the day. (00:16:35)
Visible crew/equipment: At the drive in theater, Marty says he'll put the boots on when he gets there. The camera pans to the left to follow Marty and Doc as they continue to talk. On the very far left side of the screen, the shadow of the boom mic briefly dips into frame. This happens just before Doc walks over to the DeLorean from his car. (00:16:35)
Continuity mistake: When the Doc of 1955 is about to send Marty back to 1885, he turns the time circuits on. However, if you look at the time circuits after Marty has reversed, you can see that they are turned off. (00:17:15)
Continuity mistake: When the Doc enters the destination time into the time circuits when he is sending Marty to 1885 from 1955, the time/date etc. Go in as he's typing it. However, in the previous films and later in the 3rd film when traveling back to 1985, the enter button must be pressed before anything appears for the destination time. (00:17:25)
Continuity mistake: When Marty goes back from 1955 to 1885 and meets the Indians, note that none of the Indians shoots any arrows nor do any arrow hit the car. You can see that when he drives the car back into the cave. But when he gets back to the cave after the Cavalry ride, a long arrow sticks out on the side of the car. (00:18:10 - 00:20:00)
Continuity mistake: When Marty arrives in 1885 and runs into the Indians, he comes to a slow rolling stop. But the digital speedometer on the dashboard shows that he is still traveling about 70 miles per hour. (00:18:55)
Continuity mistake: Watch the scene with the Indians (just as Marty sticks the DeLorean into reverse) and see the differences of how close and far the Indians are from the DeLorean. (00:18:59)
Continuity mistake: When Marty is being chased by the Indians, a wide shot with the DeLorean at the bottom of the screen coming towards us and the Indians following reveals the entire background for a mile or two. However, there are no cavalry visible anywhere despite the fact that they pass over the cave in the following shot only five seconds after the last Indian does. (00:19:15 - 00:20:20)
Revealing mistake: During the sequence with the Native Americans chasing the Delorean in the beginning, in one shot looking up at the sky you can see contrails from a plane, obviously not around in 1885. (00:19:25)
Factual error: When the Indians are running from the cavalry they cross over a set of tire tracks. They are too far from where Marty started so cannot be his, and the lines can't be wagon tracks because the lines are too wide and the width is uniform. (00:19:30)
Continuity mistake: When Marty is inside the cave (where he hides the DeLorean), keep a close eye on the huge landscape and very large mountains behind Marty when he is screaming at the bear. The entire background changes when he runs out of the cave to just a few hundred yards of ground before it drops down, where Marty falls into the fence. What happened to the vast landscape and mountains? (00:20:30)
Revealing mistake: When Marty and Shamus are sharing a meal at the dinner table, Shamus passes Marty the plate of rabbit. As Shamus hand moves away to let go of the plate, to the bottom right hand corner of the plate, a purple patch appears briefly where the two M. J. Fox actors interact, an error with the Vistaglide camera tech used back then. Easier to spot on Blu Ray Version, better than DVD. (00:24:10)
Continuity mistake: Watch as Seamus hands Marty the baby, there is a definite "jump" and Marty is facing in almost completely the wrong direction, looking for a clue from the set's crew as to where he should be looking to catch the baby from... (00:24:20)
Factual error: In 1885 when Maggie McFly asks Seamus for a word, they walk into the other room and behind them are a few garments hung on pegs on wire hangers. The wire hanger was invented by Albert J. Parkhouse in 1903, eighteen years later. (00:25:50)
Continuity mistake: When Marty holds the baby, the gown covers his legs. In the close-up the gown is up and the legs are bare. (00:26:03)
Continuity mistake: After visiting Seamus, Marty walks to the Hill Valley train station where a man is by the ticket window. In the next shot the man has disappeared. (00:26:35)
Continuity mistake: In 1885 Hill Valley, the hills are shown to be almost directly behind the courthouse, however in the previous films there was some distance between the two. This was likely due to the different shooting locations. (00:26:40)
Continuity mistake: When Marty is walking into the 1885 Hill Valley, he walks past an A. Jones manure hauler, which is embedded in shadow. In the very next shot, not only is he several more metres down from the hauler, the hauler is in sunlight. (00:27:31)
Visible crew/equipment: In the scene where Marty is chased out of the saloon in 1885 by Buford "Mad Dog" Tannen & his gang, in the shot showing Marty pushing his way between two women, the cameraman can be seen running along with the camera beside him to the left of the screen. (00:32:26)
Continuity mistake: When Mad Dog is hanging Marty outside the new courthouse, Doc takes aim stood in bright sunlight (when the camera is behind him), but immediately after shooting him down we see Doc from the front, stood in a large shadow. (00:33:48)
Answer: Someone would go into his barn and do what? See a sign that says time machine and believe it and then use it? Seems highly unlikely.
lionhead