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. (00:06:30)
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. (00:11:50 - 01:11:45)
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. (00:14:25)
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. (00:46:30)
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. (00:47:45)
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. (00:48:15)
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. (01:02:15)
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. (01:21:25)
Audio problem: When Taggart kicks over the fake building, he turns around and says "it's a fake, we've been suckered in." But his mouth is wide open and doesn't appear to be saying anything at all. (01:21:25)
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. (01:26:10)
Continuity mistake: When Waco Kid is lying down on hay bales 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. (01:33:50)
Suggested correction: It is true that the horse suddenly appears, but Jim is reclined on hay bales, not boxes.
For future reference, this is what the "change the entry's wording" option is for.
This entry is about the sudden appearance of a horse. It has nothing to do with The Waco Kid reclining on boxes nor does the entry say he was reclining on boxes. It says that he's reclining on bales of hay.
It did say bales of hay - I've left the correction and "change wording" comment online for a bit for informational purposes.
Visible crew/equipment: In the Rock Ridge church scene before the dynamite bundle is thrown through the church window, the device used to break the glass is visible.
Continuity mistake: When Lamarr gets out of the cab at the Chinese theater there is nobody near the cab, but when the shot of him getting out of the cab is shown, a man has suddenly appeared on the right side of the frame.
Continuity mistake: When Mongo enters Rock Ridge on the steer, the cuff on the chain around his neck instantly switches from open end facing left to facing right in the next cut.
Continuity mistake: When Taggart approaches Mongo at the fire, he pats Mongo's back with his left hand, withdraws it to clap his hands, but the next shot shows Taggart's left hand still patting Mongo's back.
Continuity mistake: When Sheriff Bart asks Jim if he can shoot the dynamite from where they are, Bart's hands are on his hips. Quick cut and now his hands are wrapped around his gun belt, close to the belt buckle.
Continuity mistake: When Taggart is thrown onto the counter in the cafeteria brawl scene, he has food slopped on his stomach, but when he slides to the cash register, the mess of food is now on his chest.
Continuity mistake: When the townspeople are saying their goodbyes to Sheriff Bart, Mongo clobbers a man wearing a derby next to him and the man falls to the ground. The next shot the crowd is still densely packed, but the man Mongo struck is not standing, on the ground, or anywhere to be seen - he has disappeared.
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.
Continuity mistake: When Mongo is sniffing Taggert's arm, his hat has been knocked down to below his eyes. When the shot changes, the hat is now lifted up above his eyebrows, even though both his hands are still on Taggert.