Episode 4

Arthur learns about Deep Thought, a computer built millions of years ago to discover the "Ultimate Answer", after 7 and a half million years, it had the answer: 42. So to decipher this answer, the builders of the computer commissioned a new, even larger computer to find the "Ultimate Question"; the Earth. It is discovered that Trillian's mice (the smartest creatures on Earth) were searching for the Ultimate Question, and they believe they can find the answer by first extracting Arthur's brain...