Treehouse of Horror XII was originally scheduled to air on Sunday, November 4, 2001. It was delayed two days when the 2001 World Series, which was delayed after the September 11, 2001 attacks and was also televised on Fox, went to seven games. As a result, Treehouse of Horror XII is one of the few episodes of The Simpsons to air in a different timeslot on American TV. Because of this, this episode ended up airing on Tuesday, making it the first episode to air on that day.
The "Burns family corpses" in the opening sequence are as follows (from left to right as seen on-screen):
A man's body that somewhat resembles General Douglas MacArthur as it's wearing an Army uniform and has a pipe and sunglasses like MacArthur's; however, it's a three-star general and MacArthur was a five-star. The body has a tomahawk stuck in its chest.
A man's body dressed as a pirate. It has a patch over its left eye and a cutlass stuck in its right eye socket.
A woman's body, dressed as a burlesque dancer (or a prostitute from the Old West), with three bullet holes in its forehead.
A man's body wearing a suit of armor with a pitchfork stuck through the helmet's eye slits.
Some of the mythical creatures that Homer and Bart caught with the Lucky Charms are: Imp, fairy, pixie (Tinkerbell), hobgoblin(Mistaken as a goblin by Bart), nymph, niad, woodsprite, Katie Couric and a leprachaun.
At the end of the "Hex and the City" segment, Homer is first seen at the Leprechaun/Gypsy wedding in his regular outfit, a white t-shirt and blue jeans. In the next scene, however, Homer is seen close-up wearing a formal blue suit.
One of the gypsies at the wedding bears a strong resemblance to Ruth Powers.
The voice of the Salesbot in "House of Whacks" is very similar to Gil's.
Lord Montymort attempts to speed up the process of removing her magical essence by turning her upside down and patting her like a ketchup bottle.
This is the second Treehouse of Horror episode that does not have the cast's names changed due to Halloween e.g. Bat Groening.
It is possible that if Harry Potter and The Philosopher Stone would aired before this episode in US, Daniel Radcliffe would make his third appearance in Season 25, since he plays Harry Potter in the film.
Skinner uses the Amnesia Dust twice at the Magic Recital: 1) To make the audience forget Milhouse's performance, and 2) To make the audience forget a bad joke he tells.
Nothing happens. The spell is presumably supposed to lift the dragon into the air, but Bart stole Lisa's wand and left a black Twizzler in its place. The dragon reveals itself to be Lord Montymort in disguise and grabs Lisa.
"Prank be undone! Destroy the evil one!"
Bart casts the spell with Lisa's wand, trying to save her by attacking Montymort, but instead he zaps himself.
The Ultrahouse suggests that Marge take a stress pill. HAL 9000 makes the same suggestion to astronaut David Bowman in 2001.
Homer disables the Ultrahouse by removing the circuit boards from its CPU, and while he does so, the Ultrahouse's voice becomes less sophisticated, then slow and garbled, and finally stops. The same thing happens to HAL 9000 at the hands of David Bowman.
The gloves on the Ultrahouses mechanical hands resemble his that are worn by Mickey Mouse.
Friends - When the Simpsons test the Matthew Perry voice for the Ultrahouse, it says "Uh, yeah, could I be any more of a house," a reference to Chandler's usual attitude.
Another voice option for the house is Dennis Miller. Marge and Lisa suggest that this voice caused murder-suicides.
Marge recalls that Pierce played the lead in Remington Steele, which the Ultrahouse confirms the first time it speaks with Pierce's voice.
Bad Taste - Homer is presumed to have been murdered by the Ultrahouse, but is revealed as having survived when he emerges from the floor. The family discovers that the back of his head is missing, revealing his brain. In Bad Taste, Derek falls off a cliff, presumably to his death, only to wake up later and notice that a piece from the back of his head is missing, also revealing his brain.
Harry Potter - Hogwarts School and various characters and themes from the Harry Potter books, parodied throughout the third segment. Harry himself appears in Mrs. Krabappel's classroom, chewing brimstone and blowing fire after she accuses him of having gum.
The episode aired a year after the publication of the fourth book, Harry Potter and the Goblet of Fire, and around the same time as the release of the first movie, Harry Potter and the Philosopher's Stone (just after the UK release and about a week before the USA release).
Mrs. Krabappel is dressed like the evil queen from Walt Disney's Snow White and the Seven Dwarfs
Nelson's line, "Stop zapping yourself!" is a parody of "Stop hitting yourself!" from Tarzan.