The skilful tactician may be likened to the _shuai-jan_. Now the
_shuai-jan_ is a snake that is found in the Ch‘ang mountains.
率然 means “suddenly” or “rapidly,” and the snake in question
was doubtless so called owing to the rapidity of its movements.
Through this passage, the term has now come to be used in the
sense of “military manœuvres.” The 常山 have apparently not been
identified.
Strike at its head, and you will be attacked by its tail; strike at
its tail, and you will be attacked by its head; strike at its middle,
Another reading in the _Yü Lan_ for 中 is 腹 “belly.”
and you will be attacked by head and tail both.