Continuity mistake: When Homer is in Lisa's classroom and imitates a farting sound, there is a sink at the back of the classroom and nobody is using it. However in the wide shot, there are suddenly two people by the sink. When the shot is back to Homer, nobody is by it.
Continuity mistake: In the scene where the Simpsons are sitting down to eat dinner, we see Bart pour tomato ketchup all over his potatoes. Then when the shot changes, we can see all the ketchup bottle and the corn has disappeared, and the ketchup has come off his plate.
Continuity mistake: When Bart arrives at school in the bus, after Homer plowed the road for the bus, the sidewalk is covered in snow except for Martin's footprints. Then, when he gets out, the sidewalk has been shovelled, as there is no snow on it. Following this, Bart is pelted by snowballs, which sends him falling face-first into the sidewalk, which is once again covered in snow.