Express a euphemistic warning. The beauty of "shaking the mountain and shaking the tiger" and "frightening the snake" is exactly the same. "Knocking" shows a threat of strength, and the target of the threat is "tiger", but it is not directly "knocking" the tiger, but "shocking the tiger" to scare the tiger and achieve the purpose of warning.
Why not just knock the tiger? China people have the virtue of "being a man leaves three points room", leaving a step for the tiger to avoid direct conflict. At the same time, it is tacit that "shocking the mountain and shaking the tiger" is a warning.
I hope it helps.