Gutei raised his finger whenever he was asked a question about Zen. A boy attendant began to imitate him in this way. When a visitor asked the boy what his master had preached about, the boy raised his finger. Gutei heard about the boy's mischief, seized him and cut off his finger with a knife. As the boy screamed and ran out of the room, Gutei called to him. When the boy turned his head to Gutei, Gutei raised up his own finger. In that instant the boy was enlightened. When Gutei was about to die, he said to the assembled monks,"I received this one-finger Zen from Tenryu. I used it all my life and yet could not exhaust it" and then he passed away.

This is the most profound koan I've contemplated.