When Moose Matson pulls up to the gas station that Chuck and Ferdie work at, his front license plate is of a white color. But when the police are chasing him in the same car, the license plate is clearly black.
The candle in Camille's room is repeatedly shown to be no more than a stub. When she takes it out into the hall it is nearly a full candle again.
After the crooks in the car shoot at him, Ferdie has three bullet holes in his hat. In the next scene at Hoskins' bus, the holes are gone.
Near the end when Ferdie is sitting at the desk and the left candle is sliding across the table, and the right candle is moving up and down, the strings used are clearly visible.
When Ferdie leaves his bedroom to go out into the hall to see who was knocking at his door, the door slams behind him. He turns around, tries the handle and pushes the door, yells, "It's locked!" and runs across the hall to Chuck's room. However, when he initially pushed on the door it clearly opened several inches; he pulled it shut, turned the handle one more time and it again opened an inch or two. It was then he yelled "It's locked!" and ran off.
During the car chase and gun battle with the police, after Moose Matson is wounded, you can hear him say, "Pull over, will ya?", but the actor's lips are clearly not moving. Also, he's firing at the police (and they are firing at him) through the back window of the car, but when he's shot he's crouching behind the back seat and under the level of the window.
When Chuck (Bud Abbott) discovers a record player in the dining area of the abandoned nightclub, he says, "At least we'll have some music". However, his lip movements do not match what he said at all.
When Ferdie and Camille do their comedy "dance" routine to the "Blue Danube", they're supposedly listening to it on the 78-rpm record played on an old-fashioned acoustical phonograph--but the sound quality of the music is identical to that of the rest of the soundtrack, without the tinny sound and scratchy background noise of a real 1941 (or earlier) record played on that sort of equipment.
Towards the end of the film, when Chuck and Ferdie are talking, there's a mirror in the top right-hand corner of the screen in which the reflection of a crew member can be seen pacing around.
When Harry Hoskins, the driver of the car that is to take everyone to the hotel, is introducing Camille Brewster to the pair, he indicates the wrong man as he says each of their names.