Revealing mistake: After King Kong destroys the train track of the oncoming train, in the POV shot directly behind the train operator while he watches Kong rise from the broken track, the small model's support control bar is visible at the right as it moves up and down. The next shot is a close-up of the shocked motorman, and after he attempts to stop the train, there's another shot facing Kong with the control bar visible for a moment. (01:31:50)
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 the two pigs run into the brick house, there is a small door at the top of the front door, which wasn't there previously. In the following shots from outside the house, this small door is missing, leaving an empty hole in the door. The hole is also shaped incorrectly. When the wolf pulls on the doorknob after trying to blow down the house, the small door appears in the hole mid-shot, then it's gone again two shots later, and the hole is now the correct square shape that it should be. (00:06:19)
Revealing mistake: When Denham is rowing the boat to the island - an obvious rear projection - the oars never touch the water.
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.
Continuity mistake: When Stan is using the smoothing plane on the piece of wood, a pot of glue is next to the bag on the table, but when Oliver leans over the table in the next shot, it is next to the saw.
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.
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.