Classicly

 Cheese market day in a town in the north of Holland. All the cheese-fanciers are out, thumping the cannon-ball Edams and the millstone Goudas with their bare red knuckles, plugging in with a hollow steel tool for samples. In Holland the business of judging a crumb of cheese has been taken with great seriousness for centuries.

The abracadabra is comparable to that of the wine-taster or tea-taster. These Edamers have the trained ear of music-masters and, merely by knuckle-rapping, can tell down to an air pocket left by a gas bubble just how mature the interior is.