Continuity mistake: When Marty McFly is being chased around the town square by Biff and his buddies in the black convertible, an extra set of lights appear under the headlights on the car (goes from a 1946 Ford to a '47/'48). (01:06:45)
Continuity mistake: After Einstein comes back Doc Brown is demonstrating to Marty how to set the time machine. He simply pushes the buttons on a key pad. To set it for July 4, 1776 he punches 3 buttons. To set it for December 25, 0000 he punches 6 buttons. To set it for November 5, 1955 he punches 12 buttons. Later, when Marty is resetting the time machine to go back 10 minutes early he punches 7 buttons (all not including the ENTER button on the keypad). (00:23:50)
Revealing mistake: After Einstein's time travels, when both flames cross Marty and Doc's legs, they cast no shadow, giving the feeling that they are floating, thus giving away the blue screen effect. (00:22:01)
Visible crew/equipment: When Marty arrives at the 1950's town and is about to be run over by a green car, the whole filming crew is reflected on its door. (00:35:40)
Revealing mistake: When Doc is using a remote control to drive the DeLorean, they show a close-up of the controller. The controller's power meter (the dial with a needle in the middle) shows no power - it's right over to the left. How's he driving with no battery? (00:20:15)
Continuity mistake: When George and Marty are talking outside the diner and George opens Marty's coke bottle for him, George's hair is all stringy and hanging down in his face. But when it cuts to another angle, it's neatly combed over to one side. (01:03:10)
Deliberate mistake: The 45's advertised as new releases on the record store sign actually came out at different times throughout 1955. A true selection of new releases from early November 1955 would have most likely included minor hit singles that 80's moviegoers wouldn't have recognized. The songs listed were some of the biggest hits of that year and were obviously chosen for their ability to help set the musical tone of the time. (00:34:30)
Factual error: Video/audio output on the JVC camcorder (if it had any at all) would not be compatible with 1955 TV. if available the camcorder output would be composite, component or COAX - all would need some sort of adapter for the audio/video to work on the TV. COAX would be the simplest, but they would need to invent the 75 ohm to 300 ohm adapter.
Continuity mistake: Marty's hairstyle changes when Jennifer kisses him on the town square bench. (00:10:45)
Continuity mistake: Before Doc's time travel demonstration, he shows Marty two synchronized clocks. Here we see Einstein turn his head towards the front of the DeLorean, but in the next frame he's facing the camera instead. (00:20:05)
Visible crew/equipment: In the opening scene, when the TV turns on as the news comes up, you can see a man with a white shirt in the reflection of the TV. (00:01:50)
Factual error: In the skateboard chase scene, after the crash, a crowd gathers. In this crowd there is a kid dressed in a Cub Scout uniform. He has a red/white town strip patch on his arm. In 1955 the Cub Scout town strip patches were blue with gold lettering. (01:07:48)
Continuity mistake: When Biff's gang arrives at the diner for the first time, Skinhead walks behind Marty and plays with a ball. When the shot changes, he is walking behind him again, but this time he is not toying with the ball. (00:38:50)
Continuity mistake: When Marty tells George how to flirt with Lorraine, they both enter the diner and Marty sits on the back of the counter but disappears between shots, only to reappear later on. Also, the extras around him change, although they're all dressed in similarly colored clothes. Check a man in a plaid jacket next to the blonde girl in pink, who disappears when Marty trips Biff. This continuity havoc was due to the combination of Eric Stoltz scenes and new Michael J. Fox reshoots.
Continuity mistake: When young George walks to Lorraine's table to read the poetic lines, the pen in front of her books moves suddenly to being on the right side of the books. (01:04:42)
Continuity mistake: When Marty enters Lou's Cafe for the first time, check a group of people gathered outside next to the doors who say goodbye and leave the place. A shot later, they're all back together, talking. (00:37:46)
Continuity mistake: At the very end of "Earth Angel", after kissing Lorraine, George waves to Marty on stage, who waves back and flexes his right hand, holding it up. It then switches to a wide shot for the end of the song, and Marty's right hand is down on the guitar again.
Continuity mistake: When Marty is holding on to the back of the truck, Biff attempts to hit him with his car. Marty quickly pulls himself to the side of the truck to avoid being hit but in the next shot, he is holding on to the back of the truck.
Character mistake: At the beginning of the movie Marty is turning on a huge guitar amplifier. The two switches for the filaments are misspelled. They are shown as "filiment." (00:03:25)
Revealing mistake: Right before Einstein is sent to the future, when a very bright light surrounds the DeLorean, not only is the dog gone, but a black bulky bag has appeared on the passenger's seat. Seemingly a hidden stunt driver or a driving mechanism. (00:21:56)
Chosen answer: I think that is *exactly* what he is thinking. He realizes that by standing up to Biff, George may have irrevocably changed his personal future, and therefore affected Marty's future as well. This is exactly the sort of thing Doc was so eager to prevent by refusing to hear any information about the future.
Phil C.