Once, when the monks of the Western and Eastern Halls were quarrelling about a cat, Zen Master Nansen, holding up the cat, said, "You monks! If any of you can speak a single word of Zen, I will spare the cat; otherwise, I will kill it!" No one could answer, so Nansen killed it. In the evening, Joshu came back from somewhere, and Nansen told him what had happened. Joshu thereupon took off his straw sandal, put it on his head, and walked off. Nansen said, "If only you had been there, I could have saved the cat!" - traditional Zen koan

Zen Master Dogen commented on this story, saying, “If I had been Nansen, when the students could not answer, I would have released the cat, saying that the students had already spoken. On behalf of the students, I would have said, ‘We are not able to speak, Master. Go ahead and kill the cat!’ That would have been a true word of Zen, and the cat would have been saved.

Dogen also said, "Or, I would have said for them, ‘Master, you only know about cutting it (the cat) into two with one stroke, yet you do not know about cutting it into one with one stroke.’”

Ejo asked, “How do you cut it into one with one stroke?”

Dogen said, “The cat itself.”

Dogen added, "An ancient master said, ‘When the great-function manifests itself, no fixed rules exist.’” Dogen also said, “This action of Nansen’s that is, cutting the cat, is a manifestation of the great function of the buddha-dharma. This is a pivot-word. Upon hearing this pivot-word, see the cat itself as nothing but the Buddha-body. Upon hearing this word, students must immediately enter enlightenment.”

Dogen also said, “This action, that is, cutting the cat, is nothing other than Buddha’s action.”

Ejo said, “What shall we call it?”

Dogen said, “Call it cutting the cat.”

Ejo asked, “Is it a crime or not?”

Dogen said, “Yes, it is a crime.”

(adapted from Zuimonki, Book 1, Chapter 6)