Humans, apparently, enjoy torturing themselves. Spiciness, after all, is not a flavour, not like sweet or salty or sour. Spicy means pain. The sensation of spiciness is the result of the activation of pain receptors in the tongue. According to psychologist Paul Rozin of the University of Pennsylvania, about a third of the people around the world eat hot peppers every single day. Why? Because they "love the burn". At a symposium on gastro-psychology during this year's Association for Psychological Science convention, Rozin pointed out that humans are the only species – we know about – that specifically seek out what would otherwise be considered negative events.

Healthy, sane humans do not stab themselves in the thighs, or bathe their eyes in lemon juice. So why do we so love to assault one of the most sensitive organs in the human body, the tongue, with what amounts to chemical warfare? Chillies are unique among foods that we should otherwise not enjoy. For example, humans also have natural aversions to the bitterness of coffee or the harshness of tobacco, but those substances have some addictive qualities, which might make them desirable. Capsaicin, the compound that provides the mouth-watering punch of chillies, does not seem to have any addictive qualities whatsoever. And yet the preference for capsaicin is almost universal; nearly every culture has incorporated it into their cuisine in some way, for milllennia.