The gag of the dog stopping from dragging his rear to say, "Hey, I'd better cut this out. I might get to like it," was originally intended to be left out of the final cut and used in the studio's yearly gag reel. Somehow it wasn't, and passed the scrutiny of the Film Board censors to be left in the cartoon.
Some prints have the final scene, when the cat shoots himself, deleted. This occurred during a period of time time when there were a rash of teen suicides. Broadcasters removed any scenes of suicides from all programming, including cartoons.
When A. Flea pulls out his "Flea Meat Chart", we can see in very small print, just below the heading, the names "Sasanoff Michael", "Bob Clampett" and "Earl Klein" (the cartoon's layout man/art director, director, and background artist)
When Elmer is reading, he is reading a Looney Tunes comic book featuring Porky Pig and Bugs Bunny.
Vitaphone production reel #1177A.