On the eleventh day of the first month, it is the "son-in-law's day", which is the day when the father-in-law fetes his son-in-law. There is a lot of food left on the ninth day to celebrate "God's birthday", except for one day on the tenth day, so the bride's family doesn't have to spend money to treat her son-in-law and daughter. The folk song is called "Eleven Begging for a Son-in-law".
In fact, "son-in-law's Day" has a long history. In ancient times, the food left over from celebrating the birthday of "God" on the ninth day of the first month has not been eaten, so these foods sacrificed to God will be treated as gifts for the second daughter and son-in-law when she returns to China. On the eleventh day of the first month, the daughter and son-in-law rushed back to their mother's house, and the elder brother or younger brother had to go out to meet them in advance to show the family's respect and attention to the son-in-law.
The eleventh day of the first month, commonly known as "Zigu Day" (in some places it is the fourteenth day of the first month). The earliest document that recorded Zi Gu was "Different Garden" written by Liu of Southern Song Dynasty. Generally speaking, Zigu is somebody else's concubine. She was jealous of the original match and was killed in the toilet on the fifteenth day of the first month. God sympathized with her and named her Ce Shen. However, people worship Zi Gu not because she is Ce Shen, but because Zi Gu represents persecuted women, so she is worshipped by women and sacrificed as a protector of disadvantaged women.