Continuity mistake: In the washroom scene, in between Gene Wilder saying "That's humorous" and "May I speak", Richard Prior is applying the shoe polish on Gene Wilder's forehead and not the nose, but next shot facing Wilder, there is no polish on Wilder's forehead but there is polish on his nose.
Factual error: After Devereaux is shot, he sees an oncoming locomotive on the opposite track coming towards him. The Streak is traveling over sixty miles an hour on its track, but in the background to the left of the oncoming locomotive, the Streak's tracks and background are stationary. Since the Streak is traveling at high speed, the forward tracks and background would not be stationary, but rushing towards Devereaux's point of view, along with the oncoming locomotive.
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.
Continuity mistake: Gene Wilder's character has uncoupled the passenger cars from the run away engine. Richard Pryor, who was holding onto Wilder from the front cars, jumps from the runaway cars to the disconnected cars. If you look closely, you can see a stage hand's arm giving Pryor a push.
Continuity mistake: At the beginning of the film, when Ned Beatty is hitting on Jill Clayburgh in the bar car, the drink in her glass refills itself from half-full to nearly full.
Plot hole: In the runaway train scene, Gene Wilder uncouples the train from the forward car, and has to make a dramatic leap to get back to the uncoupled car. Is there any reason he couldn't have uncoupled the train from the back car and just stayed put? It seems an unnecessary bit of drama.
Plot hole: When Gene Wilder is in the bar car lamenting to Ned Beatty about how wrong he's been about everything he is intoxicated. But when Beatty leads Wilder to the top of the train to prove him wrong, Wilder becomes completely sober within a matter of minutes.
Continuity mistake: When Devereaux is shot by the cop in the helicopter, he's alone in the Silver Streak's engine compartment, leaning out the open door. He's then hit by an oncoming engine. In later shots of the runaway train, there's no sign of his body or of any blood, and the door has somehow closed itself.
Revealing mistake: When George and Grover are driving on the prairie, George points out Kansas City - and the camera pans to a beautiful shot of Calgary, including the unmistakable Calgary Tower.