Heh. Old school Japanese or Korean methods. One Sensei used a shinai to whack students on the butt for motivational purposes. The bamboo would open a little on contact, and then close again, resulting in painful skin pinches that persisted long after the sting of the initial kinetic contact faded. Not one of my teachers, thankfully. Our Judo team was visiting another Dojo and we witnessed it. We never went back. Our black belts also pulled the Sensei aside at the outset and told him no shinai use on our team.