Continuity mistake: After Bugs Bunny has snipped off Elmer Fudd's pants suspender buttons, you can see Elmer's gun is directly behind him. But when Elmer picks up his gun to try and shoot Bugs, the gun is now by his foot.
Continuity mistake: When Tom traps Jerry in the blinds, he pulls the cord and squashes Jerry. At this point, you can see Tom is holding the cord, but when we Jerry sliding down the blinds in the next shot, Tom is no longer holding the cord.
Continuity mistake: During the rehearsal, Bixby throws a temper tantrum and kicks the piano. It slides straight toward the curtain, but in the next shot, it's spinning around. In the shot after that, it disappears altogether. (00:26:10)