This is the fossilised shell of a now extinct oyster from the Jurassic period. Found on the coastlines of Britain, they are called Devil’s Toenails because they look like they might possibly be just that!
It used to be believed that taking crunched up Devil’s Toenail as medicine could relieve a bad back and help cure rheumatism.
My favourite example of the devil is given in The Karamazov Brothers by Dostoevsky. He appears to one of the brothers in a hallucination. He is a gracious, dignified gentleman, educated but fallen on hard times, his clothes are tatty and run down. He says what he dreams of being is the fat 18 stone wife of a merchant “and to believe everything she believes”. Then he wouldn’t have to worry, no responsibilities or guilt, just live in luxuary and believe oneself to be a good christian “my ideal is to walk into a church and light a candle in all sincerity”. I can see the devil having that point of view, and in his well made but hole ridden shoes he would have curled deformed toenails that look very much like this.