Continuity mistake: When the crook kicks the door on a building in the fake town it falls over, but the same building falls over again when the dynamite goes off.
Continuity mistake: When Mongo first comes into town and the man on the horse says "You can't park that animal here," Mongo punches the horse and its rider, and the horse falls. Before the cut to the close up of the man (obviously the stunt double), his head is facing toward the horse's head. After the cut to the close up of the man, his body is facing the opposite direction.
Continuity mistake: When the gang rides into fake Rock Ridge, the buildings constructed by the townsfolk are two-dimensional. After the explosions begin and the fighting between the two groups begins, the structures are suddenly real. At the end of the picture the street in both towns have sagebrush and desert plants. Earlier in the movie, the town streets are clear.
Continuity mistake: When Mongo gets the "candygram", he closes his eyes BEFORE it explodes in his face. True, that is necessary for safety, but if he would have tilted his head just a little more, his hat would have blocked the view of his eyes.
Continuity mistake: The elderly woman comes to the window and gives Sheriff Bart an apple pie. He walks two steps from the window then sits it down when she taps the window again. After she finally leaves, we see a wider shot of the room, no pie in sight.
Continuity mistake: The scene where the gang stampedes through Rockridge, a thug on horseback lassos a man who is dragged down with the rope slipping down around his feet. As he's dragged foot first through the mud, he says "Well, that's the end of this suit" only now, the rope is up around his chest and under his arms and he's being pulled in a head first direction.
Continuity mistake: At the end of the movie, Harvey Korman gets pie on his face when he's behind the door in the men's room. In the next scene he has twice the amount of icing on his face as he is running across the street to hail a taxi.
Continuity mistake: When the two black workers are looking for quicksand, when Taggart and Lyle come into the scene, Charlie's hand is covered with sand, next shot as he moves around to Bart's side of the handcar it's perfectly clean.
Continuity mistake: In Jim's first scene, after he is straightened out from being upside-down, hanging off the top bunk, he reaches under the pillow for a bottle. He then finishes the remains of the bottle. The level of the liquid changes. It goes from being just above the bottom of the label to being enough for 4-5 big swallows.
Continuity mistake: When Waco Kid is lying down on boxes at the end of the film, there is no horse. All of a sudden when he's invited somewhere by Sheriff Bart, a horse appears.