There are a number of methods of opening the vaults. Most vaults, such as Harry's, use small golden keys. Higher-security vaults may have various enchantments or other measures upon the doors. For example, the door to Vault 713, which briefly contained the Philosopher's Stone, must be stroked by a certified Gringotts goblin, whereupon it melts away to allow access to the contents. If anyone other than a certified Gringotts goblin touches the door, that person will be sucked into the vault, which is only checked for trapped thieves about once every 10 years. Dragons guard the maximum-security vaults found in the lowest reaches of the bank, and a subterranean waterfall called the "Thief's Downfall" acts to overturn carts that pass through it and negate spells used by would-be robbers.