According to "Master Zhuangzi", when my master helped Wen to understand cows, he "played with a knife naturally with grace, and it was all alto", and Wen praised his skill greatly. My expert explains Dao Yun like this: I have killed thousands of cows in my life, and now it is God's will to fool people, and I have never seen the whole cow. If I cut this cow, I can do it easily. So although it has been used for 19 years, its sharpness is still "as good as new". Later, it was often regarded as a typical example of magic.

The knife used is his ox knife.