Silver bullet

[6] Some authors asserted that the idea of the werewolf's supposed vulnerability to bullets cast from silver dates back to the Beast of Gévaudan, a man-eating animal killed by the hunter Jean Chastel in the year 1767.

[7][8][9] However, the allegations of Chastel purportedly using a gun loaded with silver bullets are derived from a distorted detail[10] based primarily on Henri Pourrat's Histoire fidèle de la bête en Gévaudan (1946).

In some epic folk songs about Bulgarian rebel leader Delyo, he is described as invulnerable to normal weapons, driving his enemies to cast a silver bullet in order to murder him.

The 1941 film The Wolf Man, and its sequels and spinoffs, codified silver (whether in bullet form or otherwise) as the definitive death-dealer for werewolves, to the point where this weakness is often regarded as exclusive to lycanthropes.

The Strain novels by Guillermo del Toro and Chuck Hogan return the silver bullet to its earlier status as a weapon against the strigoi, who are broadly analogous to vampires.