Late one winter afternoon, in a field near Edinburgh, a scientist and a hunter are standing over a springer spaniel, watching it tear furiously at the base of a tree. Every few seconds, the dog ceases its digging, reaches down with its mouth and shakes a clod of earth as if it were a small mammal between its jaws. After a few minutes, the hunter, a retiree called Joyce, raises her hand and makes a circle gesture to the spaniel, Maxwell. “Snuffle,” she says. “Go snuffle the truffle.” And Maxwell takes off, whipping through the trees.