Other call boss

Albert goes into a pet shop to buy a parrot. The shop boss points to three identical looking parrots on a perch and says, "the parrot on the left costs 200 dollars". "Why does the parrot cost so much," asks the man. The boss
says, "well, the parrot knows how to use a computer". Albert then asks about the next parrot to be told that this one costs 400 dollars because it can do everything the other parrot can do plus it knows how to use the Unix operating system. Naturally, the increasingly startled man asks about the third parrot to be told that it costs 1,000 dollars. Needless to say this begs the question, "What can it do?" To which the boss replies, "to be honest I have never seen it do a thing, but the other two call him boss!"