I can imagine the scenario. Lying in her sickbed, the woman lights up her favourite brand of cigarette, a John Player Special, inhales, turns to the family and says: ‘You better put on my grave that it wasn’t smoking that killed me.’ The family take her at her word. I wish to thank her and them for giving us a laugh, albeit a rueful one. And for leaving us with a puzzle. What was it that killed her?