The pet store was selling three parrots. A man who wants to buy a parrot approaches the clerk and asks, “How much are your parrots?”

The sales clerk answers, “The first one is $1,000.”

“What does he know?”

“He knows 10,000 words and 500 sentences and can solve mathematical expressions.”

“How about the second one?”

“The second parrot costs $5,000.”

“What does he know?”

“He knows 100,000 words and 10,000 sentences, can solve mathematical expressions, and create computer programs.”

“Then what is the price for the third one?” asked the buyer.

“This one costs $20,000.”

“Really?! What does he know?”

“This one knows absolutely nothing, but the two others always call him 'BOSS’."