A bezoar — as every first year Potions student learns — is a stonelike mass taken from the stomach of a goat, that acts as an antidote to most poisons, with Basilisk venom being one notable of those exceptions. This is the reason why bezoars are used in the preparation of the Antidote to Common Poisons. This object is usually made of hair, plant fibre, or similar indigestible matter that stays in the gut of an animal and forms a hard ball or "stone".