Audio/visual unsynchronized: When the police prefect gives the order to "Round up all likely suspects," his lips clearly say, "Round up the usual suspects."
Revealing mistakes: When the building that Harpo is leaning against collapses, several of the black guide wires are visible.
Crew or equipment visible: In the scene where Rusty discovers the stolen loot, just before he moves toward the harp, the light shadow of a film crew member can be seen briefly.
Continuity: In Heinrich Stubel's bedroom, not too far from the end of the film, a lounge chair is visible by the closet, yet the next shot of the closet - the chair is nowhere to be seen.
Continuity: In the police station near the beginning of the film where the murder of the manager has been reported, there is a fan spinning above the officers' heads. Yet when the Marx brothers and Annette sneak in after escaping from the prison cells, the fan has disappeared.