The whip is a dramatic increase in velocity that occurs right at the end of the final swing. The power of slinging comes from this last quarter turn. Shown below is the crucial whipping moment. With shorter slings you do the whip on the first time around. But with longer slings like I prefer you need the speed up of the first rotation to get the velocity to a level that will support the whipping motion. I love this curved action you get from the stay during the whip.
It's hard to catch the curling of the stays on film. Shown below, after the release the stays pop and curl up on themselves like chromosomes...or maybe I should have said rubber bands.