A fellow who had spent his whole life in the desert, decides to visit a friend in the city.

He'd never seen a train or the tracks they run on.
While standing in the middle of the railroad tracks one day, he hears this whistle --Whooee da Whooee!-- but doesn't know what it is.

Predictably, he's hit and is thrown to the side of the tracks. It was only a glancing blow, so he was fortunate to receive only some minor internal injuries, a few broken bones, and some bruises.

After weeks in the hospital recovering, he's at his friend's house. While in the kitchen, he suddenly hears the teakettle whistling. He grabs a baseball bat from the nearby closet and proceeds to batter and bash the teakettle into an unrecognizable lump of metal.

His friend, hearing the ruckus, rushes into the kitchen, sees what has happened and asks the desert man, "Why'd you ruin my good teakettle?"

The desert man replies, "Man, you gotta kill these things when they're small."