An old man is selling a big cow. A young man comes to the cow and begins to look at it carefully. Then the old man goes up to him and says in his ears. "Don't say anything about the cow before I sell it, then I will give you some meat."

Then young man answers, "Because I have never seen a cow, and I wanted to know what it looks like."

"All right," says the young man. After the old man sells the cow, he gives the young man some meat and says, "Now, you can tell me how do you think of the bad leg of the cow."

"I didn't find the bad leg," says the young man. "Then why did you look at the cow carefully?" asks the old man.