A joke from the city of Khelm...

There was once an old couple owned a dog.
One time, the old man was walking the dog next to railroad tracks and the dog's leash snagged onto one of the tracks. He heard a loud whistle and saw a train zooming right towards them. Frantically, he tried freeing the dog even though the train's whistle grew louder. But alas, he had to give up and watched as the train ran over his poor dog.
The old man returned home, depressed, and told his wife what happened. The wife was deeply saddened and offered him to make some tea. She put the kettle full of water on the stove and waited for it to boil. As soon as the water began to bubble, the kettle started whistling and woke the dozing old man. Livid, he grabbed a club, stormed into the kitchen and smashed the kettle.
"What are you doing?!" His wife shrieked.
The old man looked into his wife's eyes and said:
"Gotta kill them while they're still small."
Whoever knows what the city of Khelm is, will appreciate this joke even more.