Sons and daughters are supposed to be filial and respectful to their mothers. Yet when their mother grew old, the brothers made this rule that one of them would raise his mother for one year, and if her weight dropped during that year, as a punishment for being unfilial, he would have to raise her for another year. On the eighth day of April, the day was coming when the eldest son would come to fetch his mother. The second son was apparently filial and gave the old man a lot of good food, but in fact turned his mother into a "sow". When the sow is enough to weigh, it is also the day of slaughter.
