THE FIGURE FOUR LEG LOCK WOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!
The heel hook is very dangerous. Many schools won't even teach it, or allow it to be used in sparring. Spiral fracture, and every ligament in the leg can be torn in about 2 seconds, before the recipient even feels a twinge of pain.