Continuity mistake: When Richard Pryor is ramming the police cars after saying "demolition derby", as the shot changes he is not wearing any glasses then he's wearing sunglasses, next shot no glasses, then sunglasses again, then back to none.
Continuity mistake: When George puts on Grover's purple jacket in the men's room, the collar is turned up in back. In the very next shot, it's rolled neatly down again, even though he hasn't touched it.
Factual error: When Richard Kiel is shooting at Gene Wilder on the train, you hear the "ping" of a "silencer" on the gun. However, Kiel is shooting a .357 magnum, which cannot be equipped with a silencer.