Revealing mistake: In the episode "Disorder in the Court" (1936), Moe and Larry start playing Tic Tac Toe on the prosecutor's chair with chalk and Moe first puts "X" on the upper left square. The prosecutor then sits down on the chair and when then standing up to object, the marks which copies on to his jacket from behind don't match. The "X" is gone and shows an "O" in that square where it should have copied the "X".
Continuity mistake: In the episode "Scheming Shemers" (1956), after Moe reaches into his tool bag to get Larry out of the drain, he holds a plunger in his left hand and a wrench in his right hand. The camera suddenly changes angles towards the sink as Moe arrives and now the plunger and wrench are each held now in the opposite hand instantly.
Continuity mistake: In fake Shemp episode "Commotion on the Ocean" (1956), when the Stooges first greet the large villain on the ship, Moe's hat is flat and he wears an ascot. Instantly the shot changes up close and Moe's hat is poofed up and he's now wearing a necktie instead of the ascot. This was a combination of old footage with Shemp, and a new scene filmed with just Moe and Larry (after Shemp's death). (00:03:00)