Continuity mistake: In the gala scene, Zeppo explains that Groucho is always on time and will arrive at exactly ten o'clock. Everyone starts singing the first big musical number, "When the Clock on the Wall Strikes Ten." There is even a shot of a clock set to ten. In the middle of the song, the clock strikes... six.
Continuity mistake: When Driscoll is hiding in the cliff cave with Kong above him, he moves from the front of the cave to the back two or three times without ever moving from the back of the cave to the front.
Continuity mistake: While Peggy's singing "42nd Street" for the show's premiere, she suddenly goes from tap-dancing on stage to being on top of a car's roof right in the middle of her performance. (01:24:01)
Continuity mistake: When Oliver has his hands trapped in the window frame, Stan looks at the blueprint of the Boulder Dam and the strap on Oliver's overalls is up. In the next shot, the strap is down, and in the shot after that, the strap is up again.
Continuity mistake: After Jack strangles the police officer there are 3 guys by the door - he knocks down one of the them but in the next shot there is just one man left.
Continuity mistake: The first time we see the fireman's wedding photo, she's on the left and he's on the right. The next time we see it, their positions are reversed. (00:12:05)
Continuity mistake: When Oliver's wife comes to see him in the dining room, you can see she is wearing frilly sleeves. But when she goes into the kitchen in the next shot, the sleeves have gone.
Continuity mistake: Igor's face is not disfigured on New Year's eve 1933, when he looks out at the crowd. The next scene in the morgue he is disfigured.