Continuity mistake: When two cats knock on Elmer's front door pretending to be a widow and her child, another cat pours soap flakes on them, pretending to be snow. In the shots of Elmer at the door, there appear to be no flakes falling.
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.
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 is trying to explain the money situation with Sylvester, you see that Elmer is sitting on his chair. After a quick cut to Sylvester nodding, we cut back to Elmer and he is next to Sylvester, but his chair is nowhere in sight. In the next shot, he is back on his chair again.
Continuity mistake: When Elmer opens the door to the hungry cats, you can see that there is only a handle on the door, but when one of the cats demands more money, Elmer slams the door and the handle now has a lock with it.