You kill the bear, eat the bear meat, and then put on the bearskin. The power of the bear shirt—or ber serkr in Old Norse—gives you the strength and fury of the great animal. This is what berserk means, "bear shirt." Do you actually turn into a bear-human hybrid? Maybe. Nobody liked to go to war against the berserkers, that much is known from the stories of the Roman Empire's long border conflict with the barbarians, which means not "bear brains" but "foreigners."
The human-bear combination exists in North American and Siberian tribal religions, too. These stories go back to the Bear Sons, born to an animal-god father and [...]