Describe the precise hand formation in Shuto Uke, and explain how deviations affect its ability to deflect a strike.

The precise hand formation in Shuto Uke, the knife-hand block, involves extending the hand with the fingers held tightly together and the thumb tucked firmly against the palm, forming a rigid, blade-like edge along the little finger side of the hand. The wrist should be straight and firm, creating a solid striking surface. Deviations from this precise formation compromise the block's ability to deflect a strike effectively. If the fingers are not held tightly together, the hand will become soft and unstable, reducing its ability to withstand impact and potentially causing injury to the fingers. If the thumb is not tucked firmly against the palm, it may be exposed and vulnerable to being struck. A flexible wrist will also cause a loss of power when contacted. All of these contribute to the ability of the hand to effectively deflect a strike. An improperly formed hand can create weak points that will cause the strike to land or injury the practitioner.