Ninjutsu Technique : SHUTO (open hand)

INSIDE OPEN HAND STRIKE
Swing the leading hand forward and to the outside, as though executing a back-knuckle strike. Keep the fist closed until the moment of impact, at which time you should snap the hand open, forming the "knife hand". Hold the fingers together tightly and concentrate the force of the strike on the base of the palm, just above the wrist, beneath the little finger.

OUTSIDE OPEN HAND STRIKE
Swing the leading hand forward and to the inside, as though executing a cat-paw hock. As above, keep the fist clenched until the point of
impact.

The open hand can also be used in a spear-like fashion, driving the finger tips into soft targets, such as the stomach, throat, or eyes.