 Some time ago, while at a pet store, I encountered a cockatiel who clambered for my attention. He clambered up onto my fist and began to fling himself about rather recklessly in some sort of improvised birdie boogie for a time, then stopped to judge what effect his performance had on me. I encouraged him. Again he began to jam, whipping about feverishly on my hand. Again I encouraged him. Finally he became so wrapped up and impressed