According to legend, Liu Tiemo (ca. 780-859) was born into a Chinese peasant family that lived near Mount Hua, in north central China. She was a short, plain girl who grew up helping her father farm a rich man’s plot of land. The family was poor and often hungry. When she was old enough to leave, she left.

Liu wandered through mountains and towns, often seeking shelter in convents. Eventually she asked to be ordained. She worked hard at study and meditation. After a few years she left the convent and began wandering again.

Liu Tiemo encountered nuns, monks, and teachers, and won a reputation as a fierce debater. When she met Master Zihu, he told Liu Tiemo that he’d heard she was hard to handle.”Who says this?” asked Liu.

“It’s conveyed from left and right,” Master Zihu replied.

“Don’t fall down, master,” she said, and turned to leave. He struck her.

Liu Tiemo sought out Master Guishan, and studied with him. Master Guishan was a famous teacher with 1,500 students, most of them men. Of these 1,500 he named only 43 his dharma heirs. One of these was Liu Tiemo. By now people were calling Liu “the Iron Grindstone,” because she ground to bits anyone who dared challenge her in debate. It was said she was as sharp as a stone-struck spark.

The Iron Grindstone is remembered in a koan.Iron Grindstone Liu arrived at Guishan. Guishan said, “Old cow, you came hah!”

Grindstone said, “In the coming day at Lookout Mountain (Taishan) there is a great assembly to provide monks with a vegetarian meal. Venerable, will you be leaving to go back there?”

Guishan relaxed his body and lay down to sleep.

Grindstone then left.

You can find a dharma talk explaining this mystical exchange here.