Since ancient times, a story has been passed down that a Chinese king once went to the river to fish. He saw a male crab taking care of a female crab that was in the process of shedding her shell very painfully, but after her recovery, she colluded with another male crab to kill her husband. The king immediately returned to the palace to issue this order : Any woman who dares to behead her partners will be rewarded. Soon after, thousands of women brought their spouses' heads to the royal palace. The king again issued a similar order to men. However, after a year he found that no one came to receive the reward. There was a poor farmer who went to the palace and asked the king to lend him a sword to kill his wife. But when he returned home, he heard his wife's voice lulling their child very plaintively, so he returned to the palace and asked the king to kill him because he had not completed it. The king immediately praised him and gave him a big reward.
The story is officially written like that. However, in other popular versions : Dã Tràng killed the snake's wife for adultery, so the husband gave him a blood-colored gem, which could help him understand the language of birds. Because he understood the sounds of birds, he once again helped the goose family not to be separated after an acquaintance wanted to treat him to goose meat. The geese gave him a pearl, which enabled him to walk under water like Moshe. The geese also swore that they would never eat shrimps again, because the small shrimps died in their place (the meal that should have had goose meat was replaced with roasted shrimps). Dã Tràng took the pearl without care, causing the sea to tremble, so the Dragon King condescended to give him many precious things. After that, the Dragon King lied to Dã Tràng's wife and said he wanted to marry her on the condition that she steal the gems, then brought them to the aquarium. After the incident broke out, Dã Tràng, out of anger, carried sand to fill the sea until he died. That's why there is a verse that says : Dã Tràng rolls sand in the East Sea ; Although it was very tiring but that was of no use (Dã Tràng se cát biển Đông ; Nhọc nhằn mà chẳng nên công cán gì). That's it !