It May Look Like a Walnut! - S2-E20
Character mistake: Rob is having a nightmare, part of which involves the disappearance of his thumbs. When he finds Laura at home, the script calls for him to say, "I want you to help me get my thumbs back," but he actually says, "I want you to help me get my thumb backs." His thumbs are also still there but hidden (you can see a portion of them in one frame of the episode).
Factual error: The bad guys are supposedly auctioning off the stolen Mona Lisa. But they and their prospective buyers aren't very art savvy. The painting is more than twice the size of Da Vinci's actual masterpiece. (00:44:50)
Continuity mistake: When Benny comes to Top Cat's dustbin at the start of the episode, he first pushes a door bell and then uses a handle to knock on the dustbin. In the next shot, both the bell and handle have disappeared.
Such a Nice Little Man - S3-E29
Continuity mistake: Hazel gets a glass to pour some milk. Hazel picks up the milk bottle in her left hand and begins to fill the glass from the left. In the next shot the glass is empty and a hand is shown pouring the milk into the glass from the right. (00:02:00)