At the end of our conversation she (Martha Stout) turned to address you, the reader. She said if you're beginning to feel worried that you may be a psychopath, if you recognize some of those traits in yourself, if you're feeling a creeping anxiety about it, that means you are not one.

It's not a good idea to define the boundaries of normality by tearing apart people who are outside of it.

I'm not what you'd call a fearless type of person.

Guy Savelli's role in the War on Terror began when half-a-dozen strangers, within days of one another, contacted him via e-mail and telephone in the winter of 2003. They asked him if he had the power to psychically kill goats. Guy was bewildered. He did not go around publicizing this. Who were these men? How did they know about the goats? He feigned a casual tone of voice and said, 'Sure I can.'Then he phoned Special Forces.

Sometimes labeling is only useful, like with OCD. Once you're labeled you can be treated. On other occasions labeling leads to tyranny, like with childhood bipolar disorder in the U.S.

But on the extremist side I didn't get any rejections at all. Everyone agreed to talk to me.

When I asked Robert Spitzer about the possibility that he'd inadvertently created a world in which ordinary behaviours were being labelled mental disorders, he fell silent. I waited for him to answer. But the silence lasted three minutes. Finally he said, 'I don't know.