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 discovers a letter for "Santos L. Halper", Bart has nothing in front of him on the table. In the next shot, a knife, fork, bowl and glass have appeared.
Continuity mistake: When we see Bart holding the post, he is initially holding it with one hand, but when we see a close-up of the post in the next shot, he is holding it with both hands.
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.