An arc-hand strike in the Koryo poomsae.
An Arc Hand (also called a Tiger's Mouth strike) is a hand position in which the open hand (i.e., not clenched into a fist) is held with four fingers together, the thumb spread apart from the fingers. The fingers are held slightly bent, like a Knifehand. The thumb is also bent slightly toward the little finger (the pinky finger). The striking surface centers at the webbing between the thumb and index finger, though the intent is that the impact falls on the first joint of the index finger and the thumb.