The American academic Paul Zak is renowned among his colleagues for two things that he does to people disconcertingly soon after meeting them. The first is hugging: seeing me approach across the library of his club, in midtown Manhattan, New York, he springs to his feet, ignoring my outstretched hand, and enfolds me in his arms. The second is sticking needles in their arms to draw blood.

In the event, I escape our encounter unpunctured, but plenty of people don't: Zak's work, which he refers to as "vampire studies", has involved extracting blood from a bride and groom on their wedding day; from people who have just had massages, or been dancing; from Quakers, before and after their silent worship; and from tribal warriors in Papua New Guinea as they prepare to perform traditional rituals.