"Gents Without Cents" is the classic Three Stooges short where the boys perform the famous "Niagara Falls" routine. They do it at the Noazark shipyards (It's WW2). At the end of the routine in the final "Slowly I turn..." Larry flubbed it, saying "inch by inch" twice, instead of "step by step" with Moe!
This is NOT a Slip-up! This is continuity. From the opening of Gents Without Cents they are practicing this part of the scene when the girls upstairs start dancing causing the boys problems. Larry comments "The minute we get to that inch by inch line something always happens." Later upstairs when performing the "Inch by inch" scene for the girls Curly falls into the bath tub. Larry then says "Yeah, if we ever get past that inch by inch line maybe this act would be something." (Meaning they've never made it past that line.) Later when they are being auditioned by Manny Weeks they do the "climax" (namely the inch by inch scene) Curly falls and gets the spittoon stuck on his hand. I say this is NOT a slip-up but continuity of something always going wrong at that scene.