When Moe is ready to spray the kidnappers with the water gun, a spray hose can be seen hidden under his jacket.
When Louie is thrown in the face with sand by Shemp, Joe Palma's reaction is delayed for a second.
When Shemp is caught in the hall by one of the kidnappers, he shoves him across the corridor into the wall and it visibly shudders.
You can see a odd shadow inside the top of the elevator when Dawson is knocked out by Larry.
At the conclusion, when Moe and Larry fall into a bathtub, you can see the shadow of a stagehand throwing a bucket of water through the door.