The following list of film errors and mistakes was adapted from the Internet Movie Database (IMDb.com).
1) When Prendergast is asked for his signature to turn in his gun, he’s asked to “Put your John Doe right here,” though the usual reference is to John Hancock (the most prominent signer of the Declaration of Independence).
2) When Foster shoots out the phone booth with a machine gun, a man in the background jumps off his bicycle twice, once at the end of one shot and again a second later at the beginning of another shot.
3) When Foster tells the employees to turn around and look at the picture of the burger on the Whammyburger sign, the boom microphone’s reflection can be seen.
4) At the drive-by shooting, the driver turns the wheel to the left to avoid crashing into another car, but the car careens to the right.
5) When Foster is confronted by the two Hispanic thugs, his socks are black. Earlier in the film when he is walking into Mr. Lee’s store they are white.
6) An old man who tries to escape during the Whammyburger scene can be seen dressed differently in the Mexican restaurant where Sandra and Prendergast are eating.
7) The first time Foster’s license plate is seen, it reads “D-FENS,” though when Prendergast bumps the police motorcycle the hyphen is absent.
8) Foster is first seen is wearing his seat belt, though in later scenes the seat belt is off (that’s why he’s able to chase the fly around his car).