This is pretty simple, neat, and important to any fans of the book.

1. When Arthur, Ford, Trillion, Zaphod and Marvin are on the ship and being shot at by the defenses of the lost planet, Douglas Adams writes that during the scuffle one of the crew takes a fall and bruises their right elbow. But then after making a big point about it he intentionally leaves out who it is that recieved the injury.

2. Watch the same part of the BBC tv series, they too mention it but leave it out.

3. After watching that episode all the way through, let the credits play all the way through, and after it is done, a voice will come on telling you who it was that received the injury.