At the part of the game inside a prison, where you are supposed to help the guard get accros the wall, slayers will keep spawning until you shine the light on them. If you don't use the light and let them keep coming, keep killing the slayers as they come. When your insanity hits full, keep using the main attack until you run out, and repeat this as many times as you like until your little blue bar disappears in the lower right. When done, just shine the spot to stop the slayers, and continue on your way.