[in a Drive-In, in 1955. The theater screen shows a still picture of a group of Native Americans riding horse in a desert]
Young Doc: All you have to do is drive the time vehicle directly toward that screen accelerating to 88 miles an hour.
Marty McFly: Wait a minute, Doc. If I drive straight towards the screen, I'm gonna crash into those Indians.
Young Doc: Marty, you're not thinking fourth dimensionally. You'll instantly be transported back into 1885, and those Indians won't even be there.
Marty McFly: Right.
Young Doc: Well, good luck for both our sakes. See you in the future.
Marty McFly: You mean the past?
Young Doc: Exactly!
[after a few minutes, when he uses the DeLorean and lands in 1885... an actual group of Native Americans is literally running towards his location]
Young Doc: [shouting frantically]
Marty McFly: Uhhhhh... Indians!