The Day the Earth Stood Stupid

Act I: Suck in that gut!
One day's brain flight from Earth, the planet Tweenis 12 is destroyed by a swarm of flying brains.

Meanwhile, on Earth, Leela enters Nibbler in a pet competition. After learning the prize is five hundred dollars and a year's supply of dogfood, Bender and Zoidberg get an idea. During the sheep-herding competition, the Hypnotoad displays his amazing abilities. On Nibbler's attempt, he simply devours the sheep.

Bender enters Zoidberg into the contest, claiming him to be a "Hard-Shelled Whooping Terrier". Bender forces Zoidberg through the obstacle course, then through a talent competition. Bender chases Zoidberg off with a whip.

Fry encounters what he thinks to be a novelty "floating leash", but finds it to be an actual invisible dog, which attacks him. Leela tries to get Nibbler to perform, but is unable. Nibbler sees a pig-shaped balloon and attacks. The balloon pops and launches Nibbler high into the air. He lands in a bowl of milk, splashing people with the milk and causing them to be attacked by dozens of cats.

Bender and Zoidberg get second place, losing to the Hypno-Toad, whose win may not have been legitimate. Leela and Nibbler are awarded "Dumbest Pet in Show".

Act II: I guess I'll have to eat this raw, dripping ham by myself!
Back at Planet Express, Leela accepts that Nibbler may be dumb, but Fry sticks up for him. The Professor enters with "good news" about the descruction of Tweenis 12. Hermes points out that there have been a string of such planetary destructions, and Fry (with the help of Leela) points out that Earth is next. Nibbler gets anxious and runs away.

Leela attempts to track him down, luring him with a ham. She encounters several floating brains that chase her through the alleys. She evades them, and comes upon Nibbler who is pulling a small spacecraft from a shed. He takes off, but returns when the floating brains resume the attack on Leela. Together they fly away from Earth.

Act III: I thought you were a furry little moron!
The floating brains continue their attack on the Earth, engulfing everyone in a blue glow that seems to make them stupid. Bender is concerned that his heart has stopped beating, but Fry points out that he doesn't have a heart. The Professor and Zoidberg are acting equally stupid.

Nibbler and Leela are flying through space, and Nibbler transmits his thoughts directly to Leela's brain to communicate. Nibbler explains the situation to Leela, and informs her that they're going to his home planet. Then he tells her how the universe began, and Leela realizes that every religion is wrong.

Hermes is standing with his mouth open in the shower. Fry turns on the news and finds that the news anchors are acting stupid as well. The PE crew then expresses a desire to play the lottery, buy internet stock (on margin), and join the reform party. Fry finally understands that they aren't just acting strange, but have indeed become idiots.

Nibbler and Leela finally arrive on Planet Eternium, at the exact center of the universe, and land at the Hall of Eternity, which is ten miles west of the exact center of the universe.

Other creatures that look like Nibbler are waiting inside, and greet Nibbler as "Lord Nibbler, Ambassador to Earth". However Nibbler points out that the name "Lord Nibbler" is for Leela's sake. His own name would be impossible (and time-consuming) to pronounce. One millisecond after the universe was created, a terrible enemy known as the Brain Spawn came into existence. This explanation is interrupted by the feast of a thousand hams.

Nibbler explains that the Brain Spawn are attacking all intelligent life, as they hate all consciousness; The thoughts of others are unpleasant to them. They travel from world to world, making everyone stupid to wipe out all thought in the universe. Nibbler then indicates that Fry is the hope of the universe, as he is immune to the Brain Spawn's attack.

Fry, meanwhile, tries to help the people of New New York, but foils himself.

Act IV: Time to re-educate you duncebags!
The Nibblonian fleet approaches Earth. It is explained why Fry is immune to the Brain Spawn's attack: Fry's immunity is due to his lack of the Delta brainwave, due to other events which have not happened yet. Leela is sent to instruct Fry to locate and attack The Big Brain, but she cannot be trusted to complete this task, since she'll be affected by the Brain Spawn's stupifaction rays once she lands on Earth. The Nibblonians pin a note to Leela's shirt and send her off.

Fry is attempting to educate the PE crew, but even George Washington's Head forgets who was the first president of the United States. Leela suddenly crashes through the window, and attempts to communicate with Fry, but she's been turned dumb. She hands him the note, but he misunderstands and blows his nose on it. Then he throws it in the fire, and Leela tries to retrieve it, only to discover that fire is hot. The Professor confirms her conclusion. Leela tries again to communicate, then points out the flying brains outside the window. Leela tells Fry to find the biggest brain, and Fry concludes that he might find it at the library.

Fry and Leela run to the New New York Public Library, and Fry confronts The Big Brain in the Ancient Literature room, where it is absorbing the knowledge of the human race. The Big Brain attempts to stupefy Fry, only to find him immune. Fry throws a book at the it, but the Big Brain is impervious to physical attack. Fry tries to think of another plan, and finds that his thoughts cause pain for the Big Brain. Fry frantically searches through a pile of books to find a book to make himself think. He reads the book, which causes the smaller brains outside to fall from the air. The Nibblonians prepare to land in order to clean up the mess.

The Big Brain then uses his abilities to take Fry and Leela into the world of Moby Dick. Fry almost attacks the Big Brain, but Queequeg stops him, on the grounds that it's not a white whale, but a grey thinky whale. The Big Brain escapes, and Fry, Leela, Queequeg, and Captain Ahab follow. They end up in Tom Sawyer, where they meet the eponymous character, who has tricked the Big Brain into whitewashing the fence. The Big Brain tries again to escape, and pulls everyone into Pride and Prejudice. Fry throws Tom Sawyer's whitewash onto the Big Brain, and Captain Ahab proclaims him to be white now, and he and Queequeg begin assaulting him. Fry gets an idea and jumps out the window.

Act V: The big brain am winning again!
Fry escapes from the Brain's field, and climbs a bookshelf. He attempts to electrocute the Big Brain with a broken chandelier, but crashes into the wall. A bookshelf then falls on top of him, breaking his neck. Leela tries to help, but Fry dies. The Big Brain laughs in triumph, but the Fry on the floor disappears, revealing that Fry is writing a book of his own. The Big Brain is trapped in this new book, in which Fry causes the Big Brain to leave Earth for no raisin. I mean, reason. The Big Brain falls for the trick, and flies off.

Outside, the Nibblonians "clean up" by consuming the fallen Brain Spawn. The population of Earth is returned to their normal levels of intelligence, but they process forces them to forget the entire incident. Only Fry remembers, but nobody believes him. Nibbler returns to Leela to remain in disguise until the next time he is needed to protect the universe.

Trivia

 * The planet Tweenis 12 is a reference to the fact that children aged 12 are called "tweens" because they're (supposedly) not children and not yet teens. According to the commentary, the word "tweenis" is also a synonym for a part of human anatomy sometimes called the "taint".
 * Frank Welker plays both Nibbler's animal voice and his speaking voice.

Quotes

 * The Big Brain: The Big Brain am winning again! I am the greetest! Muahahaha! Now I am leaving Earth for no raisin!
 * Prize Judge: (monotonous) All glory to the Hypnotoad!
 * Leela: (attempting to retrieve the note from the fire) Ow! Fire hot! Professor Farnsworth: The professie will help. (catches on fire) Uwahh! Fire indeed hot!

Fast Forward

 * Planet Eternium is visited again in The Why of Fry, where Nibbler again displays his ability to speak.

Characters
(In alphabetical order)
 * Amy
 * Bender
 * Debut: The Big Brain
 * Debut: Fiona
 * Dave Spiegel and Fluffers
 * Fry
 * Hermes
 * Debut: Hypnotoad
 * Leela
 * Linda
 * Debut: Ken
 * Morbo
 * Nibbler
 * Professor Farnsworth
 * Zoidberg

Episode Credits

 * Writer
 * Jeff Westbrook, Story and Teleplay
 * David X. Cohen, Story
 * Director
 * Mark Ervin
 * Voice Actors
 * Billy West
 * Katey Sagal
 * John DiMaggio
 * Maurice LaMarche
 * Tress MacNeille
 * DVD Commentary
 * Jeff Westbrook
 * Billy West
 * Tress MacNeille
 * John DiMaggio
 * Matt Groening
 * Brian Sheesley
 * David X. Cohen