Species Dossier: Mice (Pan-Dimensional Hyper-Intelligences)Copy Anchor Link

"Trillian couldn't sleep. She sat on a couch and stared at a small cage which contained her last and only links with Earth — two white mice that she had insisted Zaphod let her bring. She had expected never to see the planet again, but she was disturbed by her negative reaction to the news of the planet's destruction. It seemed remote and unreal and she could find no thoughts to think about it. She watched the mice scurrying round the cage and running furiously in their little plastic treadwheels till they occupied her whole attention."

— The Hitchhiker's Guide to the Galaxy, Chapter 14

On the planet Earth, human beings erroneously believed that they were the most intelligent species on the planet, with dolphins ranking second. In truth, both species were utterly outclassed by the undisputed masters of Earth: the mice.

Physical Form & The Laboratory MasqueradeCopy Anchor Link

• Three-Dimensional Projections: What humans observed as small, twitchy white rodents scurrying across sawdust were merely the physical, three-dimensional protruding extremities of vast, hyper-intelligent pan-dimensional beings operating from higher reality planes.
• The Behavioral Subterfuge: By allowing humans to conduct "experiments" on them—such as navigating mazes, ringing bells, and furiously running inside little plastic treadwheels—the mice subtly manipulated behavioral psychology, ensuring that it was actually they who were experimenting on humanity all along.
• Trillian's Companions aboard Heart of Gold: Prior to departing Earth with Zaphod Beeblebrox, Trillian insisted on bringing two white mice in a cage. Following Earth's destruction, these two specimens represented her final, tangible links to her lost homeworld, their tireless scurrying in their plastic treadwheels providing an oddly hypnotic diversion from galactic grief.

Commission of Earth & The Ultimate QuestionCopy Anchor Link

Millennia prior to Earth's destruction, the ancestors of these pan-dimensional beings constructed the supreme supercomputer Deep Thought on the custom-world of Magrathea to calculate the Answer to the Ultimate Question of Life, the Universe, and Everything. When Deep Thought produced the answer 42, it designed an even greater organic computational matrix—the planet Earth—to determine what the Ultimate Question actually was.

The Escape on Magrathea & Terrestrial Intelligence Hierarchy (Chapter 19)Copy Anchor Link

When the Heart of Gold landed upon Magrathea following the missile crisis:

• The Escape from the Cage: The shattering vibrations of the orbital dive damaged the cage in Trillian's cabin, allowing the two white mice to slip their confinement. Trillian burst onto the bridge in alarm ("My white mice have escaped!"), only to be met with Zaphod's total indifference ("Nuts to your white mice").
• The Three-Tier Intelligence Hierarchy: The narrator notes that her announcement would have commanded far greater urgency had the crew realized that humans were merely the third most intelligent life form on Earth, outranked by dolphins in second place and the mice in undisputed first.
• Autonomous Infiltration: Moments after the humanoid landing party disembarked, the airlock opened and closed a second time in response to an automated command that caught the ship's computer (Eddie) entirely by surprise—as the two mice quietly exited the starship under their own power to resume supervision of their ancestral homeworld.