Continuity mistake: When Principal Skinner and his mother are with Bart and his friends after the toilet prank, you can see Bart has Milhouse, Richard and Lewis are beside him. In one shot, Bart is on his own and the other three boys have gone, and in the next shot, they are back again.
Continuity mistake: In "Hex and the City", when Homer, Bart, Lisa and Maggie are eating their breakfast at the table, they see Marge with a blue beard and Homer spits some food on the table. In the next shot, the food has gone, and when Homer goes to strangle Bart, it is back again.
Continuity mistake: In "Hex and the City", when Marge, Bart and Lisa are at the Fortune Teller's office, you can see the Fortune Teller has three cards in front of her on the table. When Homer arrives, the cards have gone, and later on in the scene they are back on the table again.