Revealing mistake: When Marge is speaking on the phone to her sisters, her sisters say something that sounds like they said that Homer is ugly. Marge then puts down the phone wire that she was curling round her finger. It is easier to see this when you are using DVD, because then you can go into slow-motion, but you can temporarily see that the phone wire disappears when Marge puts it down. It is at the very end of an early scene, because as soon as this happens it changes to another scene.
Continuity mistake: When Mr. Burns comes on the P.A. system Homer started eating a donut, he takes a bite and after that the donut stays the same size even though he takes 2 more bites
Continuity mistake: In "Time and Punishment", when Homer returns to the basement after his first time travel, there is a scorch mark om the work bench where the toaster was placed when he turned it on. The angle changes to a shot from the stairs, and the scorch mark is gone. Later in the episode, the mark is back on the bench.
Audio problem: In the episode where Homer is hosting gay marriages, at one point Homer is strangling Bart and tells Lisa to hold his spot. You can hear Lisa say, "Why you little," and you can hear Bart choking, but neither of their mouths is moving.
Plot hole: In the last part of the episode, when Mr Burns is trying to convince Homer on his float to play a big prank, the timing is totally wrong. Firstly, Lisa sees the writing 'Happy Pranksgiving' on the side of Mr Burns' float way before it reaches her, and it takes Mr Burns ages to change into the Father Christmas outfit.