Claudia Wells played Jennifer in "Back to the Future." In "Back to the Future 2" it was Elizabeth Shue. At the end of the first movie Jennifer (Claudia Wells) goes to see Marty in his garage while he is looking at the black pick up. At the start of "Back to the Future 2" they start off where they left off in the first movie. As Elizabeth Shue is now Jennifer they have had to re-shoot the whole scene. They didn't quite get it right though! Marty has longer hair in the second movie, he is also wearing a watch but isn't in the first movie. There is also a car in the background but it's a slightly different car with different wheels. There are also noticable differences to when he waves his hand in from off doc's face! Quite funny and can't believe I only just noticed these mistakes!
Thanks to Ian Mack who wrote in to say that you can watch the two scenes side by side here
While Marty and the Doc are trying to get Marty's girlfriend in the year 2015, Biff steals the time machine and travels back to 1955 to give himself the sports almanac. He then returns to 2015 to leave the time machine in its place for the Doc and Marty to travel to 1985. This is not possible, as Biff would have travelled to the alternate 2015, where he is rich and owns the entire town. How is this possible? He could not have made it back to the 2015 that Marty and the Doc are in, and thus it would not be possible to return the time machine to them. And finally this would make the second half of BTTF 2 and BTTF 3 impossible - just on the basis of a sensible story line.
Contributed by: Gav Crabb
When old biff returns to 1955 and meets his younger self while sitting in his car you can clearly see that the lighting conditions were different on the days that it took to shoot each biff by the car, the day of shooting old biff was way brighter.
Contributed by: Felipe Lema
While Marty and Doc are dealing with the Jennifer issue, Biff sneaks into the DeLorean and goes back to 1955, to change history, right? HOWEVER, Biff returns to the "old" or "normal" time line, where he never had big amounts of money or a big hotel, when he shouldn't have returned where Marty and the others were, as THEY did when they "returned" to 1985. Capisce?
When Marvin Berry leaves the stage to call his cousin Chuck Berry, in Back to the Future II he stops and walks around a ladder that Mary climbed to get on the catwalk over the stage. Watch Back to the Future I and, when he is talking on the phone, there is no ladder behind him. In fact, that whole scene is different. The desk is different and the phone, and Marvin has his back to the stage in II whereas in I he is facing the stage.
You have to listen carefully but, when the Doc says "Griff's gonna ask you about tonight", he says "Biff" by accident.
As the DeLorean lands in 2015 at the start, the car has silver center caps (between the wheel nuts) in the front and back wheels, but in the next shot, they have changed back into the original black center caps.
In the original BTTF, the band leader's hand is injured when he calls his cousin, but right after Marty climbs up the ladder, you can see that both of his hands are fine.
Contributed by: Daniel Rosa Franzini
When Marty is getting hold by the corrupt Biff's men after getting back to the "alternative" 1985, his mother Loraine gets upset when Biff talks about George McFly (47m45s). Then Biff throws her to the ground.
Looking closely, Loraine shows up NOT using her pink shoe in the first shot. There is a cut, Biff punches Marty, and when the camera backs to Loraine, she IS wearing the pink shoe.