One day Mary said to her husband Bob, "Why don't we get ourselves two horses? We could go on trail rides and we can keep them in the paddock behind the house". Bob thought that it was a good idea, so the next day they came home with two horses. There was one problem, however. They couldn't tell the two apart!
Sometimes they would get confused and ride the wrong horse. They sat down to have a talk about what they could do to tell the horses apart. Bob said, "Well, I'll shave my horse's mane off, and we can tell them apart that way!" After a few months, the mane grew back, and they had the same problem. "I'll cut my horse's tail short, so then we can tell them apart!" said Mary. But, the tail grew out, and they still had a problem! So they decided to measure the horses. Bob would have the biggest one, and Mary would have the smaller one.
Guess what they found? The black one was two inches taller than the gray one!