A joke in Romance of the Three Kingdoms

Meng De has a concubine with both talent and beauty. One day, he heard that Liu Huangshu had a general named Guan Yu. This gentleman is the best all-rounder in the world, so he refused to accept it and wanted to test his talents. One day when I saw Guan Yu, my concubine drew a big circle with her hand as the stroke. Guan Yu took a look and drew a long arc with his hand. Concubine zheng, stretched out a finger, guan yu saw, then stretched out two fingers; Yuji nodded and drew a semicircle in front of her abdomen with her hand. Guan Yu saw it and shook her hand. Yu Ji went back to see Cao Cao and told Cao Cao that Guan Yu was very talented. She asked him with the rising sun first, and Guan Yu responded with the waning moon. She asked him that his talent was the best in the world at that time, but Guan Yu said modestly that he was the second learned. She praised Guan Yu, but he waved and said to Liu Bei ... Guan Yu went back to see Liu Bei and said to Liu Bei, "Why is Cao Cao's concubine so boring?" She said a big cake first, and I said a fried dough stick. " I said no, not yet ... Liu Bei felt strange, because Zhang Fei came to tell him just now that he saw Guan Yu having an affair with Cao Cao's concubine, because he saw that the concubine said she was so big and Guan Yu said he was so long. Yu Ji asked if it was enough once, Guan Yu said it should be done at least twice, and Yu Ji asked what to do if she was pregnant. The most exasperating thing is that Guan Yu said it's none of my business. ...