As the Heart of Gold speeds through “the night of space,” its passengers have trouble sleeping. To pass the time, Trillian watches her two pet mice, whom she brought from earth in a cage. While she does this, Zaphod finds himself unable to sleep because he senses something strange going on in his mind. Namely, he feels as if he won’t “let himself think about” something, but he doesn’t know what it is. As everybody but Arthur abandons the attempt to get some rest, they convene in the control room, where Trillian tells Zaphod that they’re nearing the planet he has been wanting to find. This planet, he tells Ford, is “the most improbable planet that ever existed.”
Strangely enough, Zaphod seems to be keeping something from himself. Ironically, this puts him in the same position in which he puts everybody else. He normally tries to hide his thoughts and intelligence from other people so that he has a certain amount of power or control over them. Now, though, he feels as if he’s keeping himself in the dark, thereby preventing himself from feeling in control of even his own mind.