A man goes into a pet shop to buy a parrot.  The shop owner points to three identical looking parrots on a perch and says, "The parrot on the left costs $500."

"Why does the parrot cost so much?" asks the man.  The owner says, "Well, the parrot knows how to use a computer."

The man then asks about the  next parrot and is told that this one costs $1,000 because it can do everything the first parrot can do plus it knows how to use the UNIX operating system.

Naturally, the increasingly startled man asks about the third parrot and is told that it costs $2,000.  Needless to say, this begs the question, "What can it do?"

To which the owner replies, "Honestly, I've never seen it do a thing but the other two call  him boss!"