Continuity mistake: In "The Thing and I", when Bart, Lisa and Maggie are in the attic, Bart picks up a book and on the front cover it shows a picture of Homer with the words "Homer, I Hardly Knew Me" by Homer Simpson. But when we see Bart with the book in the next shot, the front cover is now completely clear.
Continuity mistake: In "The Thing and I", when Lisa and Bart watch their father go to the fridge, you can see the spoons in their bowls are pointing to the left, but after a quick cut to Homer getting the fish out of the fridge, we cut back to Bart and Lisa and the spoons are now pointing to the right.
Continuity mistake: In Lisa's music class, there is a wide shot of the entire class. Üter sits next to Milhouse Van Houten in this shot. However, in the next shot, it's Ralph Wiggum. In a following shot of the entire class, it's Üter again. They both replace each other in the same seat.