Frogs

Frog myths are as old as humans. One widely held superstition was the “Toad Stone”. It was supposed to be a jewel found inside a toad’s head. When placed in a ring or necklace, the jewel would heat up or change color when it detected poison, which protected the wearer from evil doers.

In Shakespeare's play "As You Like It", the Old Duke says, "Sweet are the uses of adversity which, like the toad, ugly and venomous, wears yet a precious jewel in his head."