Continuity mistake: When Laddie is eating the meat that Bart gave him, Santa's Little Helper's bowl is next to his bowl. When we see Laddie two shots later, there is now only one bowl, and in the shot after that, there are two bowls.
Continuity mistake: When Bart sees "The Covet House" order in the catalogue he has picked up from the trash can, he is reading it with both pages open, but when we see him in the next shot, he is reading the catalogue with the back pages folded under.
Continuity mistake: When Bart is at the Card Shop, he picks up the magazine "Zoidzilla" and put on the top of the pile he is holding. But when he takes the pile to the cash desk, the front cover of the magazine is now coloured green.
Continuity mistake: When Marge finds Lisa's German verb wheel in the post during the breakfast scene at the start of the episode, you can see Lisa has nothing in front of her. In the next shot, a bowl and a glass have appeared.