“Somehow I measure my life and longevity not in years but in the number of accumulated experiences,” he says. Many of these experiences are mountains he has climbed. One is finding a use for an extremely powerful magnet at a university in Holland in the late 1990s. He levitated a frog, and even though this demonstrated nothing new about magnetism, it attracted grants, attention and job offers. It marked him out as a prankster and earned him an Ig Nobel prize from Harvard. Against the advice of more self-important scientists he showed up to collect the prize and, the organisers remember, “was constantly running around telling dirty jokes”. He was especially fond of showing the kind of imagery to be obtained from the reflection of two fingers in a spoon.