What does it mean that my father-in-law looks at his daughter-in-law's ashes?

Su Dongpo lost his wife in middle age and never married. On this day, his daughter-in-law wore a white gauze skirt as transparent as cicada's wings, walked up to Su Dongpo with a teacup and whispered, "Dad, please have tea!

Su Dongpo looked at his daughter-in-law's pink face, graceful posture and affectionate eyes, and suddenly got a little carried away. Just when he was in high spirits, he suddenly remembered that this was his daughter-in-law blushing at once. Daughter-in-law asks: "Why does father-in-law blush?"

Su Dongpo did not answer. He picked up the teacup and quickly wrote two poems on the table with his index finger: "If there is a pipa in the green gauze account, it is spring." Because Su Dongpo was lazy and didn't clean the table for a long time, there was a thick layer of ash on the desktop, and the handwriting was very clear.

After reading it, the daughter-in-law quickly wrote two more sentences with her finger: "If the father-in-law plays a song, the fat water will not flow out of the field." After writing, I ran away with a red face.

Su Dongpo gloated when his son came back. Seeing his father so happy, he asked, "Father, what do you see?"

Su Dongpo got a fright. He quickly wiped the handwriting on the table with his sleeve and said, "I don't see anything." I am picking up dust. " From then on, whenever there is an affair between the old man and his wife, and between his sister-in-law and his brother-in-law, it is said to be collecting ashes.