Visible crew/equipment: When Bart enters the saloon to deliver the candygram to Mongo, his shadow can clearly be seen against the painted backdrop behind him depicting the street scene.
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.
Visible crew/equipment: In the beginning when the two black workers are using the handcart to look for quicksand, you can see the cable pulling them in one quick shot.
Audio problem: Towards the end when everyone is running around the studio lot fighting, there's a tour group getting ready to enter the cafeteria. The tour guide's mouth doesn't even remotely match what she is saying.
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: 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: 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: 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.
Deliberate mistake: It's obvious that the wagon train that has to form a circle has dummies as passengers. A none-too-subtle Brooks visual gag.
Audio problem: When Hedley shoots a man for chewing gum on line the sound effect of his body hitting the ground takes place about a full second before he actually collapses.
Revealing mistake: When Mongo wakes up and breaks free of the chains, in the shot where he breaks free, the chains suddenly shift position and some even disappear. This is because the camera was stopped and the chains were replaced with fake break always before the camera was restarted. Another way to see this is because the water that dripping down Mongo's face suddenly stops.
Deliberate mistake: In the beginning, when the two black workers are using the handcart, they bend their arms as they crouch down to give the illusion that they are slipping into the quicksand.
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.