A guy walks into a bar looking frustrated. The bartender asks, "What's the matter?"
The guy replies, "Well I've got these two horses and I can't tell them apart. I don't know if I'm mixing up riding times or even feeding them the right foods."
The bartender suggests, "Why don't you try shaving the tail of one of the horses?"
The guy says, "That sounds like a good idea, I think I'll try it."
A few months later, he returns to the bar in worse condition. "I shaved the tail of one of the horses, but it grew back and I can't tell them apart again!"
The bartender says, "Why don't you try shaving the mane?"
A few months later the guy is back. "I shaved the mane of one of the horses, but it grew back!"
The bartender yells, "Just measure the damn horses. Perhaps one is slightly taller that the other one!" The guy storms out of the bar.
The next day, the guy runs into the bar. "It worked, it worked!" he exclaims. "I measured the horses, and the black one is two inches taller than the white one!"