hair-trigger (n.)

1795年； 比喻用法始于1841年。Hair 可能是指激活所需的轻微压力。

The difference between a hair-trigger and a common trigger is this—the hair-trigger, when set, lets off the cock by the slightest touch, whereas the common trigger requires a considerable degree of force, and consequently is longer in its operation. [Charles James, "Military Dictionary," London, 1802]

“发条扳机”和“普通扳机”的区别在于——发条扳机在设置后，只需轻微触碰即可放开扳机，而普通扳机需要相当大的力量，因此操作时间更长。[查尔斯·詹姆斯，《军事词典》，伦敦，1802年]