Plot hole: The Winslows' younger daughter, Judy, disappeared from the show in 1993 (halfway through the series' run) with no explanation.
E-I-E-I-(Annoyed Grunt) - S11-E5
Plot hole: When the Simpsons run away from the duel, they go to Homer's childhood farmhouse. But Homer and Grandpa burned the farmhouse down in the episode "Grandpa vs. Sexual Inadequacy".
Rent-a-Pop - S2-E7
Plot hole: After the meeting with Zack's "fake Dad", Mr. Belding informs Zack he wrote a letter to see the Dad again... However when the "real" Dad sees the fake "Belding" (whom the Dad didn't know was fake), the Dad never questioned about the "seeing him AGAIN" letter when this real Dad never met Belding before. In addition, wouldn't the Dad question this letter to Zack anyway?
Hone made aishite? Akane koi o fukuzatsu kossetsu - S1-E5
Plot hole: Dr. Tofu is able to tell that Ranma was hit by a softball (he says something about the marks like he actually sees them), but Ranma's wound is still covered by the bandage, that he'll remove in the next episode. This is linked to a larger mistake in the following episode. (00:19:55)