According to another source, once Xuanwu had begun his study of the Way, he discovered that he must purge himself of all of his past sins to become a god. He learned to achieve this by washing his stomach and intestines in the river. Washing his internal organs, his sins dissolved into the water in a dark, black form. These then formed into a black tortoise and a snake who terrorized the country. Once Xuanwu learned of this, he returned to subdue them as in the other story.