Continuity mistake: At the show the school puts on in "Wiz Kids", when the Montymort Dragon is first seen in the cage, the cage has 6 bars at The Front. When Lisa says "Release The Dragon", the cage has 4 bars. When the cage door is being raised, it has 6 bars again. (00:18:45)
Continuity mistake: By the vending machine, Lisa first points her card at the cell on the right, then there's a zoom on the cells and we see her hand starting to point again, but this time at the cell in the middle. In the next shot, she lowers her hand with the card, which however in this shot is pointing at the cell on the right again.
Continuity mistake: Homer is on The Front lawn when the bus of tourists turn up and Mario comes out. Homer gets mad and throws trash cans at Mario, who runs away and climbs up into the tree house which is at the side of the house, but it should be at the back.
Continuity mistake: At the beginning of the episode, Homer slides down a big pipe and smashes through one of the windows on the right side of the car. But when Homer crashes into the chestnut tree, it is fully repaired. (00:01:25)
Continuity mistake: As Mr. Burns and Smithers are talking on the phone, we see a hand holding the receiver, and when they're finished, the next shot shows us a black skinned referee. His skin color was yellow before. Also, the phone is nowhere to be seen. (00:15:55)
Continuity mistake: As Bart is about to enter his house after trying to impress his friends by krumping, you can see he is entering The Front door. However, in the next shot when he gets inside and Marge is waiting you can see that he has entered the family room, which is only accessible through the back door. Entering by The Front door would place him by the stairs, at The Front of the house.
Continuity mistake: When we see the overhead shot of Krusty crying at the Simpsons' table (just before he explains his story), we can see that Krusty has no meat on his plate. When we first see the family and Krusty after the story, there's meat on Krusty's plate. This is visible in the 'Homer's tuxedo' mistake picture.
Continuity mistake: When Mr. Burns falls onto the sundial, everybody starts gathering around. Marge is there, with Maggie. She left Maggie in the car and seeing as she went off to look for Homer, Bart, Lisa and Grandpa and that she was one of the first on the scene when Mr. Burns collaspses, it would be difficult to run back and get Maggie from the car.