Revealing mistake: In the last third of the film just after the announcement that Kong is coming, a native jumps out of his hut, loses his balance and falls by a chicken coop. His wig comes off and gets caught on the fence.
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.
Revealing mistake: When the woman at the bar brings Jack the mustard which she forgot, Jack puts his napkin in front of his mouth. A fraction of a second before that, you can see the down-side of his face which should be invisible. Instead of nothingness you see it's all black. That is material used for the special effects, but they didn't 'make it invisible'. (00:06:50)
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: In this 1933 Mickey Mouse short, Mickey dreams he is in a mad doctor's castle. He opens an inner door and finds a second door behind it. He then finds a third, fourth and fifth door. When a sixth door swings open and he is able to enter the mad doctor's lair, the other five doors have vanished.
Revealing mistake: When Denham is rowing the boat to the island - an obvious rear projection - the oars never touch the water.
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.