Treehouse of Horror XV - S16-E1
Continuity mistake: At the beginning when Kang and Kodos's boss comes to have dinner, his stomach explodes leaving a hole, yet in the next shot the hole has vanished. (00:00:40)
Home Away From Homer - S16-E20
Continuity mistake: When Homer rings the doorbell of the Flanders' former house to visit the new neighbour, it moves downwards on the door frame. In the first shot it lines up with the gap between the lock and the doorknob, but in the next shot it is beside the doorknob, and in other shots in the episode the doorbell isn't even there. Also, the glass panels on both sidelights line up with the door differently between shots.
Treehouse of Horror XV - S16-E1
Continuity mistake: Ned hammers in the For Sale sign; a few shots later, when Homer comes, it is no longer there. (00:03:40)
Revealing mistake: In the opening sequence's parody of the series where Bart becomes fat and comes out from school on his skateboard, he theoretically should go down the stairs, instead his silhouette suddenly climbs up on the wall next to him, revealing a mistake in the post-production's animation. (00:06:05)