Adder stone

One holds that the stones are the hardened saliva of large numbers of serpents massing together, the perforations being caused by their tongues.

I have seen that egg as large and as round as a common sized apple, in a chequered cartilaginous cover, and worn by the Druids.

It is a badge which is worn with such ostentation, that I knew a Roman knight, a Vocontian, who was slain by the stupid emperor Claudius, merely because he wore it in his breast when a lawsuit was pending.

The Glain Neidr of Wales are believed to be created by a congress of snakes, normally occurring in spring, but most auspicious on May Eve.

The Mabinogion, translated into English in the mid-nineteenth century by Lady Charlotte Guest, mentions such stones on two occasions.

In Russian folklore, adder stones were believed to be the abodes of spirits called Kurinyi Bog ("The Chicken God").

Kurinyi Bog were the guardians of chickens, and their stones were placed into farmyards to counteract the possible evil effects of the Kikimora (The wives of the Domovoi, the house spirits.)