When the professor slips on a bottle Curly threw on the floor to make him fall, an open set of teeth mysteriously appears on the floor when he falls down.
There are devices and targets to where the plank of wood is supposed to fall when Larry is leaning it against the wall, but when the wood plank hits Moe on the head, all the devices/targets have disappeared.
When Curly drops the rolls of wallpaper on Moe's foot, it is clear that Moe moves his leg before it happens.
Moe almost breaks character when Curly says the line, "The man liked my looks".
When the Stooges run out of the room while Igor the gorilla is still firing the machine gun upside down, it is clear that the actor inside the costume is just mimicking the movements from the gun even though the sound effects are heard and the gun is not loaded.
When Moe and Curly are going at it again, Larry warns them by saying, "Jiggers, the boss." They all get back to work and the boss walks in. But Larry couldn't have seen anyone coming because the wooden door is closed, and there are no windows in the door or walls.
When Larry tries to open the bedroom door to escape, the knob comes off in his hand and the door does not budge until the professor opens it. It is unknown why the door would be able to open if there was no knob on the other side.
When the professor rushes Mr. Beedle from the lab, he calls him Mr. Biddle.