Continuity mistake: When Judge Doom is melting and is just about to die, the wide angle shows he's surround by a very thick cloud of yellow smoke that keeps us from seeing his face, then in the close-up it changes to a very thin smoke that allows to see his face, and then back to the wide angle and the thick smoke again. (01:31:55)
Continuity mistake: Roger and Jessica are safe when the spray-machine breaks the brick wall. It then goes through the other side staying on the left side and moving far away from the debris. Angle on Valiant, and when back to the wall the machine has suddenly moved several feet to the right and is crossing the wall again.
Continuity mistake: In the scene where Valiant leaves Maroon's office, he goes outside and closes the door behind him all the way. Then a cartoon character passes him. Notice the character opens the door by pushing on it instead of turning the knob? I thought Valiant closed it all the way. (00:08:45)
Factual error: In the bar scene where Judge Doom is looking for Roger, there is a pinball machine that can be seen on the right side of the stairs as Roger and Eddie are running out of the bar. Electromagnetic pinball machines of this design were not around at the time of this film's setting. The pinball machine is a Gottlieb Hurdy Gurdy (1966) model.
Factual error: When Doom reaches into the cab of the Dip vehicle and starts it, it doesn't jump. It is a modified military vehicle, and it's a standard. If you try to start a standard vehicle without pressing the clutch in to disengage the gears (the weasel driver left it in gear when he died), then the vehicle would lurch forward as the engine turned over.
Factual error: The red cars are seen traveling with poles raised on both ends. The wheel at the raised end of the pole, which collects power from the wire, must always be trailing the car. Basically, streetcars going forward have the rear pole raised and front pole lowered, and vice versa. They would not be traveling at normal operating speeds with the front pole raised, as that would damage the wiring system.
Continuity mistake: The number of wood slats on Baby Herman's playpen keeps changing at the start of the film. When his mom says goodbye there are eight slats at the front, and five at the side. When he escapes the playpen there are eight at the side, and when Roger realizes the playpen's empty, there are nine at the side and seven at the front. Additionally, the characteristics of the teddy bear changes, as well as the colors of the balls on the wood slats. (00:00:40)