Suddenly there is a festive tail wagging, and a little spade digs into the earth in the exact spot  where the nose of your trusted friend is pointing… Today dogs are used for digging truffles, but for centuries pigs were used. In fact, the sows. Guided on a leash by farmers, they were capable of finding a truffle even ten feet underground: they are attracted by odours that resemble sexual hormones secreted by male pigs.  Until the end of the last century, an iron ring was wedged at the front end of the snout to stop them from immediately devouring the truffle. The first document that describes using a sow was written by the humanist Bartolomeo Sacchi, who in 1468 highlighted the technique used for hunting truffles in Umbria. The first trace of a professional "truffler" is in a document accounting for the financial regulations of Spoleto, from August 22 nd 1400, in which the merchandise that entered and left the city was annotated. Already by then, truffles were very precious: to distribute them outside of the territory, you needed to forego a "payment by the pound" duty. If you're thinking of turning your hand to this art, you should know that the "truffle dogs" typical of Umbria, which unite both physical force and docility, have been selected in the Valnerina valley over the course of centuries: the Black Valnerina Grifo, a rustic dog accustomed to working in both cold or humid weather, has a natural ‘talent' and it's almost unnecessary to train them