At Hogwarts, Harry begins learning wizardry and also discovers more about his past and his parents. Harry inadvertently makes Gryffindor's Quidditch (a sport in the wizarding world where people fly on broomsticks) team as a Seeker, learning that his father was also a member of the team. One night, he, Ron and Hermione find a giant three-headed dog on a restricted floor at the school. The dog is guarding the Philosopher's Stone, an item that can be used to grant its owner immortality. Harry concludes that his potions teacher, Severus Snape, is trying to obtain the stone in order to return Voldemort to a human form.