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"The Yeerks. We've learned they've used several fronts to purchase an animal testing laboratory and a meatpacking plant."
Erek King[src]

The Experiment, published in March 1999 and written by Amy Garvey based on an outline by K.A. Applegate and Michael Grant, is the twenty-eighth book in the Animorphs series. It is the fifth book narrated by Ax and his third book as sole narrator.


Official Description

The Yeerks have decided to try a little experiment. They've decided that if they can develop a way to make people more "willing" to be infested, they can speed up Earth's invasion. So, the Yeerks try to invent a substance that will take away the human ability to make a decision. A substance that will eliminate free will.

Now the Animorphs and Ax are not only faced with trying to slow down the Yeerks' invasion, but they also have to try and put an end to the genetic testing on a small group of humans. This time there's only one chance to stop the Yeerks. And if anything goes wrong, it's all over...

Plot Summary

This section requires expansion

Ax and Tobias in cattle morph, Cassie in her morphing outfit and Jake as a peregrine falcon

The Animorphs find out from Erek that the Yeerks have taken control of a meatpacking plant and a laboratory. They acquire chimpanzees and infiltrate the lab. They don't find very much information so Tobias and Ax morph into bulls (thinking they would morph into steer but not realizing that the DNA does not include surgical procedures) to go to the meatpacking plant. Inside the plant, they discover a room with humans in cages. The computer tells them that it is an experiment designed to destroy the free will of the human population so that the Yeerks can take over easily, but a Yeerk scientist eventually confirms that the experiment was a total failure.



Supporting Characters:


Other Characters:



Major/Highlighted Events

  • Ax constructs a home for himself in the national forest outside Cassie's farm, containing a television with cable access, and spends his free time watching various programming and using television as a medium to learn more about human society. After becoming enamored with television, especially soap operas and infomercials, Ax begins to update his personality and speech patterns based on what he sees on TV.


Morpher Morphs acquired Morphs used
Jake Chimpanzee Peregrine Falcon, Seagull, Chimpanzee, HouseflySiberian Tiger
Rachel Chimpanzee Bald Eagle, Seagull, Chimpanzee, HouseflyGrizzly Bear
Tobias Chimpanzee, Bull Human (himself), Chimpanzee, Bull
Cassie Chimpanzee Osprey, Seagull, Chimpanzee, Flea (possibly; partially), Housefly, Wolf
Marco Chimpanzee Osprey, Seagull, Chimpanzee, Great Horned Owl, Silverback Gorilla (Big Jim), Housefly
Ax Chimpanzee, Cow, Bull Human (Main), Northern Harrier, Seagull, Chimpanzee, Great Horned Owl, Cow, Bull


  • The front cover quote is, "Change can be a good thing. A very good thing....".
  • The inside cover quote is, "Got Milk?" which is an obvious reference to a famous ad created by Goodby Silverstein & Partners.
  • This is the seventh book in which all the Animorphs acquire the same new morph.
  • Marco suggests that they go to the mall and see how many cinnamon buns Ax can eat before he explodes, with Ax replying that he has already performed this experiment. This is a callback to The Decision where Ax ate an entire pan of buns at the mall.
  • Jake tells Marco to drive since he has experience, with Cassie moaning that she doesn't want his experience brought up as her father still mourns the destruction of his truck. This is a reference to the events of The Andalite's Gift.
  • The interior illustration is notably the only time in the series where one of the Animorphs (Cassie) is depicted wearing a typical form-fitting morphing outfit, rather than normal street clothes.
  • The book came with two bookmarks featuring the cover morph of Ax morphing a cow.
  • The regular edition came with two bookmarks of Ax morphing a cow, while the Scholastic School Market Edition contained an advertisement for the Animorphs Alliance fan club instead.
  • ANIBASE: The ending for this book made some Animorphs fans hopping mad. This is what Katherine Applegate had to say about the controversial closing scene:
"I took some grief for this from the fans. A fair number were upset that I ended with all of the Animorphs ordering hamburgers. I am in favor of being as humane as possible in dealing with livestock, but I'm not a vegetarian. I kind of think that I'll start worrying about the treatment of cows more once there are no more political prisoners, no more children dying of curable diseases, and no more fanatics blowing themselves up to murder civilians."



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Graphic Novels #1 The Invasion | #2 The Visitor | #3 The Encounter | #4 The Message | #5 The Predator | #6 The Capture