Moray eel. When I lived in Greece I was out fishing one morning and someone speared a moray eel on a sort of trident. He was appalled, rapidly pulled the eel from the tines and through it back into the water in disgust. Since I have often used moray eel in soups and stews I was very disappointed to see it go, but the two fishermen were adamant that it was a "dirty fish" which crept onto the land to mate with snakes.
