A river flows eastward. What does a yellow joke mean?

A spring river flows eastward. Yellow jokes mean like. According to relevant information, the story of a river flowing eastward began in Wuzhen, a water town in the south of the Yangtze River in the 1930s. Zhang Zhongliang, who followed Master Wu's family since childhood, and Maid Sufen were childhood friends. Master Wu, who is devoted to the Tao, married an eight-room aunt just to make a great contribution to the practice of returning to Yang. At that time, he caught his son's sweetheart, Zilun, and the father and son turned against each other, which led to his family leaving home. Wu Bao, the housekeeper, and four aunts plotted against Zilun several times. Zilun tried to escape from the Wu family, but Su Fen became aphasia after being beaten. In order to prevent element fragrance from becoming the ninth aunt of the Wu family again, Zilun failed to assassinate and was tied to the gallows. Fortunately, she was saved by the Qi family who came back in time. Finally, a big fire helped Zhong Liang and Su Fen. They arrived in Shanghai by boat overnight.