The Fat and the Furriest - S15-E5
Factual error: Homer creates a giant sugar ball by making a normal sized cotton candy on a paper cone, and then coating it with liquid caramel. The cotton candy holds its shape and Homer continues to expand it with more cotton candy and caramel. However, cotton candy dissolves very quickly and tears apart easily. Between the weight and moisture content of the caramel, the original cotton candy would have immediately melted and/or collapsed.
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Factual error: The symbols on the heads of the Teletubbies on stage are wrong. They did use the word 'teletubbies', so they're meant to be the same as the real world. (00:05:40)
Margical History Tour - S15-E11
Factual error: Lisa, as Salieri, says she has wine for sale : "Claret, Port, Riesling ...". All three glasses on her tray are filled with red wine. Riesling is a white wine.
Margical History Tour - S15-E11
Factual error: On the castle where King Henry VIII is supposed to live, the flags at the top have the pattern of the English flag, being a + shaped cross on a coloured background, but it should be a red cross on a white background. Instead it's a white cross on a blue background. Those are the colours of the Scottish flag, but England and Scotland were separate countries at that point in history. And the cross on the Scottish flag is an X shape rather than a + shape anyway.
Factual error: The tongue Lisa sleeps on in the museum isn't anatomically correct. It shows the bitter and sweet taste buds as being side by side on the surface of the tongue. In reality, different taste buds are not in specific places on the tongue. I wouldn't normally complain, but this is supposed to be in a museum.
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.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.