Who knows? Throw a stone to break through the underwater sky. Next sentence?

Su Xiaomei teased the groom three times.

Qin Guan appreciates Su Xiaomei's talent and wants to marry him. Su Xiaomei wrote a couplet: Open the window and close the door to see the moon. Su Xiaomei's brother Su Shi was worried about his brother-in-law, so he reminded Qin Guan that he threw a stone into the water, and the Qin Guan team set a bottom line: throw a stone to break through the underwater sky.

This kind of story is included in Feng Menglong's Sanyan, which is very interesting.

This is just a couplet. Throwing stones to break through the bottom is the next sentence of the couplet, and the last sentence is to open the window to explore the moon behind closed doors.