There is a curious habit of bears that is well known but not well understood. When walking along one of his trails, a bear will stop at a certain tree, tear it with his teeth and claws, rub his back and head against it as high as he can reach, even with the tip of the nose, and standing on tiptoe. There is no doubt that a bear coming to such a tree can tell by the scent whether another bear was there, and whether that bear was a male or a female, a friend, an enemy or a stranger.