A werewolf in folklore and mythology is a person who shapeshifts into a wolf, either purposely, by using magic, or after being placed under a curse. The medieval chronicler Gervase of Tilbury associated the transformation with the appearance of the full moon, but this concept was rarely associated with the werewolf until the idea was picked up by modern fiction writers. Most modern references agree that a werewolf can be killed if shot by a silver bullet, although this is more a reflection of fiction's influence than an authentic feature of the folk legends. A werewolf allegedly can be killed by complete destruction of heart or brain; silver isn't necessary.