The other day I went to do my weekly chores, one of which was picking up and setting new mouse traps if needed. It turns out that today was an unlucky day for a certain rodent. I grabbed myself a new mousetrap after cleaning up the carnage from before, and began to set it. Now that I've set many before it does not seem too hard anymore, but it still requires a lot of care when handling one, since it could seriously injure an appendage if set off accidentally. I thought about it and realized that a mousetrap is really just a balancing act with equal torques on each side (F*r = F*r). The way a mousetrap is made it uses a two-lever system, in such a way that a small force exerted on the bait will trigger the trap and thus kill its worthy victim. The arm lengths have much different lengths, in that L1<<L2 and d1<<d2. Therefore, even just a tiny extra force at the bait will be able to trigger the trap. This is why it takes so much less work to fix the trap than to set it off.