A Hag Stone, also known as an adder stone, is a stone that has a naturally occurring hole through it. Such stones were, and sometimes still are, believed to have magical properties. These supposedly include the ability to heal a snake bite, or see through the disguise of a witch or fairy by looking through the hole.*
 
Length - 38mm
 
*Horniman Museum and Gardens (2021) - Vicky King - Hag Stones and Lucky Charms