A form of foot torture used by the Chinese in which the victim's foot was placed between three pieces of bamboo and systematically squeezed WordNet 3.0 & Open English WordNet

The jiagun ankle crusher was a Chinese instrument of torture consisting of three wooden boards approximately a yard in length that were connected with cords, which when placed around a suspect's feet and gradually pulled, caused agonizing pain in order to force a confession. Wikipedia

A form of torture, among the ancient Chinese, in which planks of wood squeeze or hit the victim's feet. Wiktionary