A group named "In Defence of Animals" organized protests against a poster for the film that showed a cat in a dryer. They also complained about a scene in which a cat's legs are hurt by Junior.
The only actor to appear in all three films and the short-lived cartoon series was Gilbert Gottfried. Jack Warden appeared in all three films, but not the cartoon.
When Ben steals Roy's Wagoneer, he intentionally drives over some flowers in a neighboring yard. This is due to deleted footage that involved a subplot of the woman who owned that house getting fed up with the Healy cat going to the bathroom in the flower bed. Although every other trace of this subplot is removed from the movie, this scene was left in (the deleted footage appears on edited TV versions of the movie, but isn't on the DVD).
At the last scene on the bridge, after Ben got shot, you can see the wheel of the overturned car turning in some frames and then be completely still the next, and then moving again a few seconds later.
When Ben is standing on the bridge watching the truck drive away with his wife in the back, he has the rifle in his hand. Ben and Junior turn around to walk back to the car and the rifle disappears. It seems unlikely he would have left it laying on the bridge.
Big Ben Healy: [about Junior being adopted]
You don't know what you're letting yourself in for. For all you know the kid is liable to end up in the looney bin. He might even be democrat!
Junior: [voiceover, on a stormy night a woman is carrying a basket]
Nice night to be born. Apparently my birth is not considered a blessed event; that's me in the basket, and that's my mother carrying me.