A man who had spent his whole life in the desert visited a friend. He'd never seen a train or the tracks they run on. While standing in the middle of the railroad tracks, he heard a whistle, but didn't know what it was. Predictably, he was hit and thrown to the side of the tracks, with some internal injuries, a few broken bones, and some bruises.
After months in the hospital recovering, he was at his friend's house attending a party. While in the kitchen, he suddenly heard the tea kettle whistling. He grabbed a baseball bat from the nearby closet and bashed the tea kettle into an unrecognizable lump of metal. His friend, hearing the ruckus, rushed into the kitchen, saw what had happened, and asked the desert man, "Why'd you ruin my good tea kettle?"
The desert man replied, "Man, you gotta kill these things when they're small."