When Curly Howard shakes himself after falling into the plaster, there isn't any plaster in his hair, but when the night guard turns around to see Curly behind him, Curly's head is completely covered in plaster.
The bait on the hook in Curly Howard's stomach is whole after he had clearly chewed it up in his mouth.
As Moe Howard and Larry Fine are backing towards each other while Curly Howard is in the middle, a noticeable jump cut occurs in the film, then Moe suddenly appears in a different position.
After Moe Howard pulls the fish out of Curly Howard, the X-Ray machine is off, but you can still hear the noise it's making.
After water sprays out of Curly Howard's mouth the first time and hits Moe Howard, you can hear this strange loud squeak sound that most likely came from the source of water that was hidden behind Curly's mouth.