Jerry is eating Swiss cheese when he points to Tuffy, who is off-screen. The camera glides over to Tuffy holding a vase. Only it's not Tuffy: it's Jerry again.
When Tom runs over the tacks, there are four stuck in his foot. When he gets outside, there is only one.
Near the end, Tom is shown locking all the doors to the King's room and swallowing the key. When jabbed in the nose, he can't get out to scream because all the doors are locked. After the King finally goes back to sleep, Tom ushers the mice out the door so they can resume fencing. That couldn't happen if the doors were still locked.