[Chang Yu tells us that by noting the joy or anger shown by the enemy
on being thus disturbed, we shall be able to conclude whether his
policy is to lie low or the reverse. He instances the action of Cho-ku
Liang, who sent the scornful present of a woman’s head-dress to Ssu-ma
I, in order to goad him out of his Fabian tactics.]
Force him to reveal himself, so as to find out his vulnerable spots.