Snap down drills are closely related to the hands-to-feet motion on back handsprings required to add power and turn over to the rebound connecting a handspring to another  handspring or to a somersault.  The goal is to open the shoulder area and then pushing from shoulders and wrists snap the whole body into a deep hollow while turning on one unit from hands to feet.   /Still1/ Shoulder Opening.  /Still2/ Straight up handstand.  /Still 3/ Shoulders opening.    /Still 4/  Aiming for hollow turn over down.