Continuity mistake: When Apu awakes, he has a closed note pad, and the table looks small. In the next high-angle shot, Apu's book is open and face down, with paper on top of it and a pen beside it. The table is also bigger, with Bart sitting there with his breakfast things too.
New this week Continuity mistake: When Lisa goes to save Clara, she's wearing the same dress she took to the dance, but after Clara walks safely back to land, Lisa is wearing another outfit entirely, then changes back to her previous outfit in the very next shot, then back to her unknown outfit seconds later.
New this week Revealing mistake: After Lisa says "For a product that's evil and deadly" while standing in front of the tomacco stand, there's a duplicate Lisa behind her that stands still while she moves, giving Lisa the appearance of having two heads. It looks like the animators made a mistake while trying to animate Lisa.
Continuity mistake: Lewis changes from black to yellow when Milhouse dares Bart to pull Santa's beard off.