The Ziff Who Came to Dinner - S15-E14
Factual error: When the SEC guys break up the poker game they arm their guns in the same manner you would with a shotgun (there is even the shotgun cocking sound effect) yet they are M-16 style weapons and would not need to be armed this way.
Catch 'em If You Can - S15-E18
Factual error: Bart gets bored of "Love Story" and presses the split-screen button to watch Krusty, which replaces the movie audio with the Krusty audio. Split-screen buttons only provide a picture, not an audio.
The Bonfire Of The Manatees - S17-E1
Factual error: Alec Baldwin, as an expert on manatees, says that they are also called dugongs. Manatees are found in Atlantic coastal waters and in the Amazon and tributaries. The dugong is a distinct species found in the coastal waters of the Indian and southwest Pacific oceans.
The Last Of The Red Hat Mamas - S17-E7
Factual error: Milhouse says he speaks fluent Italian, but his Italian is full of basic grammatical errors. He says that "insegnante" means "masculine teacher" when the same word is used for a male or female teacher. There are errors in Lisa's Italian course too ("barca piccola" instead of "piccola barca"). Despite Lisa's understandable mistakes, as she is a learner, Milhouse never corrects her (there is no such word as "idioto"). Even Milhouse's grandmother, who is Italian, makes many grammatical mistakes.
Factual error: Moe has a double barrelled shotgun that fires four times. A double barrelled shotgun can only fire two shells before having to reload.
Factual error: In the episode with Donny, when Bart sees principle Skinner go into the school to meet with the rat, the door is backwards. The bars that are pushed in to open a door are always on the inside.
I Don't Wanna Know Why the Caged Bird Sings - S19-E4
Factual error: During Dwight's attempted bank robbery, he gets hit with a couple of dye packs, then appears a few shots later totally clean. The dye packs banks use are notoriously difficult to wash off once they're triggered; even if Dwight did manage to clean himself up, there would still be remnants of dye on him.
Treehouse of Horror XVIII - S19-E5
Factual error: In the Mr. And Mrs. Simpson segment Homer is firing a minigun at Marge and three of the barrels are seen spitting fire. A minigun however only uses one barrel at a time to fire.
Factual error: The cover of "World's Finest Comics" #94 is shown on the wall at the comic book store. It features Superman with a sign that says, "Gotham or Bust," and Batman gulping. The actual cover of "World's Finest Comics" #94 shows Superman being sprayed with liquid kryptonite while Batman and Robin catch sight of him.
The Burns and the Bees - S20-E8
Factual error: When the bees fly to Mr. Burns' stadium, they are shown as seeing the stadium with 11 eyes. Bees only have 5 eyes. (00:18:15)
Factual error: In the scene where Lisa's great great grandmother, and the slave Virgil escape to Canada, they enter Canada across a suspension bridge, which has, on the Canadian side, the Canadian Maple Leaf flag. In 1860, Canada was not yet even a country, and the flag was the Union Jack and the Canadian Ensign. The Maple Leaf was not adopted as the Canadian flag until February 15, 1965.
Holidays of Future Passed - S23-E9
Factual error: When Lisa is trying to find Zia on the internet, the Google design shows Doctor Seuss because it is his birthday. Doctor Seuss' birthday is March 2nd. This takes place on December 24th.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.