Continuity mistake: When Elmer slams the front door after being tricked by one of the cats, you can see that the door has a handle and lock on it. But when the cat dressed as a salesman leaves Elmer's house later on, look at the door and you can see that it has now changed to a door knob and keyhole.
Continuity mistake: When Elmer kicks out the cats after marching into his home, you can see there is nothing on the bottom part of the door. When we see the cats surrounding the house in the next shot, the bottom part now has an "X" on it.
Trivia: When we see a cat looking through the dustbins at the beginning of the cartoon, there is a newspaper on the ground that has "Foster" on the front page - a reference to the Warner Brothers story writer Warren Foster.