A farmer was having trouble telling his horses apart.

"I have two horses that I can't tell apart," he tells his friend. "Is there any way you can help me?"

"Shave the mane off one horse," his friend said. "Then you'll know the difference between them."

The farmer did as he was told, but after some time the mane grew back and he couldn't tell the difference anymore.

"This time, give one of them a small cut on its leg," said his friend. "Then you can tell it apart from the other."

The farmer did this again, but the other horse ran into a thorn bush and got a similar cut on its leg.

"Measure their height," said his friend. "One of them must definitely be a bit taller than the other."

The farmer tried it out, and it worked. Ecstatic, he ran back to his friend's house.

"It worked!" he yelled. "The black one is two inches taller than the white one!"