The Fisherman and his Soul

In 'The Fisherman and his Soul', a young Fisherman finds a Mermaid and wants nothing more than to marry her, but he cannot, for one cannot live underwater if one has a soul. He goes to his priest, but the priest tells him his soul is his most precious possession, and the soulless mermen are lost. He tries to sell it to merchants, who tell him it is not worth anything. He goes to a witch, who tells him his soul is his shadow, and says how it can be cut away with a viper-skin knife after he dances with her.