The press had given him the nickname worm man', but his friends knew him as Derek. Scientists had manipulated his DNA to mimic one of the most amazing features of the common or garden worm: the ability to regenerate lost tissue. And it had worked. When they chopped off his hand to test him out, a new one had regrown within a month.

Then it all went wrong. His body was slowly deteriorating. To save his life they had to transplant his brain into a new body. However, a major mistake during the operation severed his brain in two.

Fortunately, both halves fully regenerated and both were successfully transplanted into new bodies. The only problem was that both the men who now had one of the brains believed they were Derek. What is more, both had Derek's memories, mental skills and personality.This created problems for Derek's boyfriend, who couldn't tell them apart. It also led to the Dereks getting entangled in a legal battle to claim Derek's-assets. But which was the real Derek? They couldn't both be him, could they?

--From Baggini, J. 2005. ''The Pig that Wants to be Eaten: 100 Experiments for the Armchair Philosopher.'' London: Penguin Group.