A man walks into a pet shop to buy a parrot and asks the owner what he has.
"This one here is rather special - he costs £10,000" says the shopkeeper.
"Ten grand for a parrot??!!! What's so special about him?"
"Well," replies the shopkeeper, "he doesn't just repeat words, he can hold conversations about philosophy and psychology!"
The man decides to check this out and is surprised to find himself having a decent chat about existentialism with the parrot. "Amazing", he says, "have you any others?"
"Well this one here is £20,000" says the shopkeeper as he produces a 2nd parrot.
"Twice the price? What does this one do?" asks the man.
"This one is not only a good conversationalist, but is fluent in French, German and Spanish too" replies the shopkeeper.
"Blimey," exclaims the man, "What about this one over here?"
"My God! What does this parrot do?"
"Well, not a lot as far as I can tell," explains the shopkeeper, "but the other two call him 'Master'"