It was apparently of a jocular nature, for he felt impelled to slap his leg again and cram his fist into mouth.
因为他感觉被迫又击打他的腿，把他的拳头塞进嘴巴里。

He must needs break a leg just before we go on holiday, ie It was a foolish action causing great inconvenience.
我们正要去度假, 他却偏偏摔断了腿。

The horse should be slightly bent in the direction in which it is moving and bent around the inside leg of the rider.
马体稍稍的往行进的方向弯曲，围绕骑手的内方脚。

if drinking water due to thirsty and the leg becomes thin and has fat liquid in the urine, it is called kidney elimination.
若渴而不饮水不绝, 腿消瘦而小便有脂液者, 名曰贤消。