三十六计 Thirty-Six Stratagems: 打草惊蛇 Stomp the grass to scare the snake
Chapter 3: Attacking Stratagems 攻战计
During the Tang dynasty, the bookkeeper of an unpopular magistrate called Wang Lu received a letter from the local people accusing him of corruption. Wang Lu wrote on the letter 'by merely beating the grass, you have startled the snake hiding within'. This perhaps implied that he recognized the ploy, and was ready to fight back. Maybe also he realized that the stratagem had worked well as a warning to him that the population would not stand for his corrupt ways.
When startled, a person's fight-or-flight reaction is triggered where they may retreat, fight back or even freeze, like a rabbit in the headlights of an oncoming car. What they will actually do may be unpredictable, which makes this stratagem one that should be used with care.
Do something unusual, strange, and unexpected as this will arouse the enemy's suspicion and disrupt his thinking. More widely used as "[Do not] startle the snake by hitting the grass". An imprudent act will give your position or intentions away to the enemy.