Da Situ met Cao Cao alone, and Cao Cao said that Dong Zhuo could be killed by a strategy of presenting a knife to kill people, so Wang Yun gave Cao Cao the treasured knife in his collection for convenience. The next day, Cao Cao went to see Dong Zhuo and said to Dong Zhuo, "The horse is too late." Dong Zhuo ordered Lu Bu to choose a good horse to give to Cao Cao. Dong Zhuo lay sideways on the couch. There was a flash of a knife in the middle, and he immediately reprimanded Cao Cao. At this time, Lu Bu also came back, and Cao Cao knelt down and raised the knife.