Continuity mistake: At the end of the movie, when the spray-machine breaks the brick wall with the word 'Keep Clear' painted on it, the first 'E' and the 'A' get destroyed, but appear rebuilt a second later.
Continuity mistake: In the climactic scene where the Red Car is about to "Dip" Roger and Jessica, one shot of Eddie (shot upward from the ground) also includes the hook that Roger and Jessica are hanging from. However, Roger and Jessica are not animated into this shot.
Continuity mistake: At the very end of the movie, when the cartoon characters start singing "Smile Darn Ya Smile" together, Just before the scene changes, the cartoon background is gone. When the cartoon characters lets Eddie, Roger and Jessica go to Toontown, the background reappears.
Revealing mistake: When Eddie fires his "Toon" revolver at the whisky bottle, you can see what appears to be a white, plastic model in his hands. This obviously would've been used as a reference for the animation to be tracked onto later.
Revealing mistake: During the climax, one of the weasels says "Toon Town's right on the other side of the wall, boss!" If you look, you can see a brick moving completely by itself behind him. It literally just pushes out of the hole in the wall as though it's being pushed from the other side. It seems like the other weasel was supposed to be animated pulling it out, and they somehow forgot to animate that part. (He does reach over and grab it for a split second... but then immediately lets go for some reason).
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 Eddie throws Roger into the bar's storeroom (after Roger was breaking plates on his head), there's a Lucky Strike ad poster with the slogan "Be Happy, Go Lucky." However, the Be Happy, Go Lucky ad campaign didn't start until after 1948 when BDO took over advertising, and the film is set in 1947.
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.
Revealing mistake: In some shots with the red cars, such as when Benny, Eddie, and Roger are about to crash into one, look at the wheels. The trucks appear raised with a third, large wheel in the center, obviously a road vehicle outfitted to look like a streetcar.
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: While Valiant is driving through Toon Town, there's no continuity between what he sees ahead, and what is seen in the car's rear window seconds later.
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.
Factual error: Eddie Valiant borrows Deloris' camera to photograph Jessica playing "Patty Cake". There were at least 13 photos from a roll of film that could make only 6 or 8 shots.
