When Homer is eating the fish pieces in the restaurant one of the pieces keep reappearing after he has eaten it.
The clock reads 7:00 when the kids enter for dinner, but switches to 5:00 after Marge mentions sushi.
When Marge is looking up at Homer saying "He's alive!", Homer's beard is yellow like the rest of his face, instead of light brown.
Fugu poisoning doesn't proceed in the manner Dr. Hibbert claims; what actually happens is that paralysis sets in almost immediately, resulting in eventual death from asphyxiation when it reaches the lungs. However, Dr. Hibbert's mistake in this matter forms the entire basis of this episode.
Bart and Lisa both claim that sushi is raw fish. This is a common misconception; raw-fish dishes are sashimi, sushi (which can be made with raw fish, cooked fish, vegetables etc.) are vinegared-rice dishes.