I'm at some kind of dinner party, and find myself sitting opposite a silver-haired, self-possessed man. I am told by a neighbour that he is a GP, whose particular party trick is being able to guess how long people are going to live. "What about steepholm?" they ask him. He looks at me appraisingly, and says that given a fair wind I may still have 20 years left in me.
"But then I'll only be 67!" I gibber. "I'm in good health, I've never smoked, I don't drink much these days, I come from a long-lived family, and have no inherited diseases that I'm aware of. How do you come up with that figure?" (My voice gets shriller as I go on.)
He just looks at me with a kind of patronizing pity, as if he would like to explain, but knows I wouldn't understand the medical technicalities.