The Open Hand
The second major hand form is the open palm, the infamous "karate chop," known as the shuto or "knife hand" in Okinawan styles.
This form of the hand is generally known in Kungfu as a "lotus palm", with the thumb outstretched along the fingers. If the thumb is cocked tightly in a fist form position, it is known as the "willow palm". While this hand form can be used directly, either thrusting with the fingertips or striking with the little finger edge of the palm, it is more commonly used in Shuai Chiao in the "standing palm" form.
The Standing, or "Willow" Palm
Here, the little finger edge of the palm is used to press on and attack specific acupuncture points, as in the basic "Chopping Throw", or used as a general blocking and parrying technique to draw the opponent's extended limb into a grasping hold. The Open Palm hand is much used in Shuai Chiao: by placing the fingers and thumb together, the hand becomes a unified object that is quite resilient to strikes and blows.
If the fingers and thumb are separated, it is very easy to have a finger "snagged" by an opponent's kick or punch, resulting in a sprained or broken finger. By keeping the fingers and thumb together the flexiblity, softness, and sensitivity of an "open-hand" style can be maintained while still having a robust hand-form that can withstand a direct strike.
A variation of the willow palm is the "corrugated palm", much used in the Tai-zu style as an attacking hand-form. Here, the hand is arched across both its width and length and somewhat tensed to create a stronger striking weapon.
With this hand form, the fingertips have more support, and the back of the hand arches the major metacarpals into action for offensive or defensive strength.