S1·E4 Episode 4

Arthur learns about the Great Project - the second most powerful computer in existence, called Deep Thought, created to answer the Ultimate Question of Life, the Universe and Everything. The computer comes back online much later on to give its final answer - 42.

The scientists are understandably hacked off, even more so when Deep Thought cannot tell them what the Ultimate Question is, and a new computer, called the Earth, has to be built for that purpose.

The current owners of the Great Project, Trillian's pet mice, want to cut open Arthur's head to find the Question, but when the crew are all trapped behind a bank of exploding computers, all appears lost.