In 2 pictures, Lisa is seen with lesbian partners.
Sideshow Bob is depicted as dead for the second time this season, the first being in the (admittedly non-canon) "Treehouse of Horror XXII".
It would appear that Lisa turned goth but than went to dress up as Sailor Moon.
Even though, according to Ned, Edna has been 'accidentally killed' by Homer before this episode, she is still in the list of people who want to 'friend' Lisa.
When Lisa sees the "Google" type she says it's Dr. Seuss' birthday. However it's Christmas time and Dr Seuss' birthday was March 2nd.
In the view of London of the future, Daleks from "Doctor Who" can be seen as policemen on the streets.
Despite Maggie being the most famous singer of her generation, her voice is never heard in the episode.
Bart has married (and divorced) his high school girlfriend Jenda, who was previously seen in the sixteenth season episode "Future-Drama".
This is the second time adult Maggie does not talk, the first time was back in "Lisa's Wedding".
Featured music: Sleigh Ride by The Ronettes.
Show Title: Sleigh bells ringing as reindeer fly Santa Claus' sled in the air. However, it's evil alien Kang dressed as Santa shouting "Ho, ho, ho!"
Billboard Gag: Bah Humbug & Happy Hanukkah: Christmas Ignorers United (with Mr. Burns and Krusty the Clown's rabbi father pictured).
Chalkboard Gag: Cafeteria Trays are not toboggans.
Couch Gag: Instead of the usual couch gag, the Simpsons are seen in the form of gingerbread cookies rushing to lie down on a Christmas-themed plate with a hand placing a "For Santa" note next to it. Homer likes his cookie form so much, he bites off his left arm.
The title is reference to the Moody Blues album Days of Future Passed.
In one of the photos, Lisa is dressed as "Sailor Moon".