A monk asked Chao-chou, "Has a dog the Buddha Nature?" Chao-chou answered, "Mu."23
Here the word mu, meaning "nothingness" or "un," is an elegant resolution of a perplexing Zen dilemma. Had Chao-chou answered in the affirmative, he would have been tacitly instigating a dualistic view of the universe, in which a dog and a man are allowed to be discussed as separate objects. But to have responded negatively would have been to even more strongly betray the Zen teaching of the Oneness permeating all things. An answer was called for, but not an explanation. So the master responded with a nonword—a sound that has been adopted in later Zen practice as symbolic of the unity of all things.
This wisdom made Chao-chou such a legend in his own lifetime that many monks from the south came north to try to test him, but he always outwitted them, even when he was well past a hundred. Perhaps it would be well to round out his story with a garland of some of the exchanges he had with new monks:
A new arrival said apologetically to the master, "I have come here empty-handed!" "Lay it down then!" said the master. "Since I have brought nothing with me, what can I lay down?" asked the visitor. "Then go on carrying it!" said the master.24
One day Chao-chou fell down in the snow, and called out, "Help me up! Help me up!" A monk came and lay down beside him. Chao-chou got up and went away.25
A monk asked, "When a beggar comes, what shall we give him?" The master answered, "He is lacking in nothing."26