A man went into a pet shop to buy a parrot. He was shown an especially fine one which he liked the look of, but he was puzzled by the two strings which were tied to its feet. “What are they for?” he asked the pet shop manager. “Ah well, sir,” came the reply, “that’s a very unusual feature of this particular parrot. You see, he’s a trained parrot, sir, he used to be in the circus. If you pull the string on his left foot he says ‘Hello’ and if you pull the string on his left foot he says ‘Goodbye’.” “And what happens if you pull both strings at once?” “I fall off my perch, you fool!” screeched the parrot.