A hag stone is a stone with a naturally formed hole through it, also known as an adder stone, fairy stone, holey stone, serpent egg, or witch stone. They are often found on beaches, rivers, and streams in Europe, particularly in Northern Germany and the United Kingdom. Hag stones have been used for many religious and spiritual purposes and are believed to have magical properties. They are thought to protect against evil spirits, ward off witches, and offer good luck and healing. The hole in a hag stone is believed to allow only good things to pass through, while bad luck and evil thoughts are too big to pass through the hole and become stuck in the middle. Hag stones are still used today by modern witches and pagans, who often wear them or keep them in handbags and pockets as good luck charms. Some of the uses of hag stones include hanging them above the front door or over a window to keep evil spirits out, tying them with rope to a ship to prevent witches from clinging to the vessel, and attaching them to bedposts or barn doors to stop witches from souring milk or taking horses for a gallop in the night.