When humans walk or skip on uneven surfaces or steps, their ankles can rotate freely and make most of the soles to contact with the ground before the bodies losing balance.

• 人在不规则地面，台阶等地面行走或跳跃时在失去身体平衡之前脚脖可以向各个方向旋转使脚掌大部分与地面接触。