Continuity mistake: Before Mr. Slate takes a picture of his employees, Sandy (the one that Fred gives a hot foot to) is standing by two other men. When Fred gives Sandy a hot foot, the men have disappeared, and when we see the photo that Mr. Slate has taken, they are back again.
Continuity mistake: In the scene where Mr. Slate asks his employees to gather round for a group photo, Fred decides to liven up the situation by giving Sandy a 'hot foot'. When Mr. Slate takes the photo, Fred is lighting the match on Sandy's foot, but the picture that comes out of the camera shows him not lighting the match at all.