Ants.

So I have ants on my desk at work. Not huge ones, just little tiny ones. And not swarms, just a few crawl by a day. I don't know what to do about them, really. I put a couple traps down, and I've made sure there's no food around for them to find. Still they march ever onward, in search of that which they will not find, destined only to meet their untimely end by my Wrathful Hand.

The killer inside me, long dormant since I moved away from Queens (where things like this used to happen), has reawakened. I kill without remorse; I kill without pause.

I've noticed something strange about the oozing corpses of my foes. They smell like nail polish remover. At first, I had assumed that that the smell was coming from elsewhere. But as the bodies piled up, it became abundantly clear. It was my own lethal hand that smelled of acetone. My own, unpolished hand.

So yeah. Apparently this isn't news to anyone who hangs out with ants a lot, but it was news to me. My first guess, which wasn't too far off, was that I was smelling a very concentrated amount of the chemical ants use to make trails other ants can follow. It turns out ants produce a lot of chemicals other than that one, and what I'm really smelling is a cocktail of all those different acids, that just kinda happens to smell like acetone to me. Thanks, Internet!

Money quote from The Straight Dope: "That smell coming off those crushed ants is not just the smell of fear and death, but also the smell of true cleanliness and health." Read the whole explanation to find out why.