For many people, it's the scraping of nails on a blackboard. For my wife, it's the scraping of knives on dinner plates: a phenomenon I frequently - albeit unintentionally - cause. Everyone, it seems, has their own, personal trigger for becoming a shuddering slave to crawling skin. I once witnessed someone flee a room because an egg box was introduced to it, such was her morbid fear of touching such ovum containers.
My own nemesis is the feeling of dry, untreated wood, of precisely the kind they use to produce complimentary spoons in a well-known chain of sushi restaurants. I genuinely cannot have dessert there without borrowing some children's cutlery from one of my daughters. My wife openly and quite correctly mocks me for this, so I scrape the children's cutlery on my plate. I don't really. They serve food on plastic dishes there. Maybe this is why.
There is one excruciating agony upon which my wife and I do agree. Our youngest has, after several tiring weeks of trying, produced two top front teeth to complement the bottom ones which emerged a while ago and now sit proudly clear of her gums. Our delight at the hiatus in the sequence of sleepless, screamy nights that this development promised, has quickly been tempered by our daughter's new habit of grinding her new teeth against her older ones.
AAAARRRRRRGGGGGGGGHHHHHHHHHHHHHHHHHHH etc.
What makes it really sinister is that you hear it before you see it. Scrape, scrape, scrape. 'What's that curious noise?' you may think to yourself, glancing enquiringly around the room in search of its source. The terror rises gradually as it dawns on you that the youngest of your beloved family is thoughtfully sliding her lower jaw from side to side against her upper jaw, happily oblivious to the abject mayhem caused by her actions. The realisation of the cause of the noise - like a vicious kazoo, made of knives, inside your brain - seems to increase its volume until you simply cannot bear it.
Invariably this results in screams of defeated anguish from one or both of her parents. And she sits there smiling at us.
I'm thinking of pulling her teeth out.