Debuting in Season 2 of The Simpsons, "Treehouse of Horror" has evolved into an annual tradition for the long-running animated series. A collection of vignettes and satires of horror stories and sci-fi conventions, the episodes have remained a fan-favorite convention of the show as it's grown and changed over its three-plus decades on the air.

Notably, Futurama (in many ways a sister show to The Simpsons and currently due for its third revival on Hulu) initially had its own version of the "Treehouse of Horror." While it lacked the holiday cogitation, it was also a pretty horror-centric half-hour of animation. But after two entries, the "Anthology of Interest" concept was more or less abandoned -- partly because Futurama, as a show, didn't really need its own "Treehouse of Horror."

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'Anthology of Interest' Was Futurama's Version of 'Treehouse of Horror'

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"Anthology of Interest" was the sixteenth episode of Futurama's second season. Pairing Chris Louden and Rich Moore with a trio of writers, the episode focuses on Prof. Farnsworth's newest invention, the What If Machine. Fry, Bender and Leela in turn ask the machine a question, prompting a short non-canon vignette playing out the scenario. The episode got a sequel in Season 3, which followed a similar trajectory and played with overt parodies of early video games and The Wizard of Oz. By contrast, the first "Anthology of Interest" effectively plays out as a series of quietly scary subversions made for dark comedy -- very similar to "Treehouse of Horror."

Each segment features plenty of death and mayhem -- "Terror at 500 Feet" recasts Bender as an invading robot from space, destroying much of New New York, and killing Zapp and Kif before being brought down by a giant radioactive Zoidberg. "Dial L for Leela" sees a more assertive Leela give into some surprisingly vicious impulses, eventually murdering the entire crew save for Fry. "The Un-Freeze of a Lifetime" is an early hint at the show's true mythology, and ends with Fry's dim-witted defiance of fate causing the complete collapse of the universe as we know it. They're each fun, dark takes on colorfully silly series, a fun Futurama answer to The Simpsons' annual Halloween special. But as Futurama continued to evolve, it highlighted why it didn't necessarily need its own "Treehouse of Horror."

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The Core Difference Between The Simpsons & Futurama

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The Simpsons, by its very nature, is rooted to reality. While it's become increasingly cartoonish and features plenty of zany unbelievable storylines, it's ultimately a show about a family doing their best to thrive in a jaded American town, with monetary concerns, marital strife, and existential dread complicating the bizarre and happy moments in life. The "Treehouse" Specials -- completely removed from those purposeful limitations -- get to break all previous conventions. The ultimate difference between Futurama and most shows in general, but especially The Simpsons, is that it could break conventions every episode. The far future setting and cartoonishly advanced technology made the universe an increasingly flexible place, where histories could be retconned with ease, and any setting that could be imagined could be explained.

Unlike The Simpsons -- which thrives when it gets to break the rules -- Futurama breaks the rules on a regular basis. It didn't need an annual chance to do so, when each episode can casually send Bender to college, introduce a planet exactly like rural Scotland, or unveil lost truths of the universe. Episodes could become extended parodies of sci-fi conventions or play with the very laws of the universe, and still be part of the show's evolving canon, thanks to the way the world had evolved to embrace any concept. Even hard rules in the universe on concepts like time-travel were subverted frequently -- with the show even poking fun at itself for this trend in later seasons.

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Why Futurama Doesn't Need a 'Treehouse of Horror'

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This isn't to say Futurama gave up on the anthology formula entirely, but it stepped further away from tales of terror and further embraced overt parodies. Like with the later "Treehouse of Horror" specials, the grounded framing device connecting the nominally non-canon episode to the main series was removed. Instead of playing up the characters for horror as in the original "Anthology of Interest" episode, later anthology episodes like Season 6's "Reincarnation" or Season 7's "Saturday Morning Fun Pit" were direct parodies of animation styles (like "Reincarnation's" extended riff on early anime conventions) or trends in older cartoons (like the extremely violent G.I. Joe parody in "Saturday Morning Fun Pit").

Futurama's format speaks to the uniquely flexible world created by the show's embrace -- and frequent subversion -- of countless sci-fi inspirations and scientific explorations. Futurama evolved into a thoughtful and often-times purposefully weird show that could switch genres, play with tones, and remain focused on the distinct and fleshed-out central cast. It's an interesting comparison to The Simpsons, which also evolved and expanded but never forgot the baseline rules that define the show -- an element the show has even quietly mocked about itself. As such, The Simpsons still needs "Treehouse of Horror" to become fully untethered. Because Futurama already operates on that level on a regular basis, however, the show doesn't really need its own "Treehouse of Horror."