The great Taoist master Chuang Tzu once dreamt that he was a butterfly
fluttering here and there. In the dream he had no awareness of his
individuality as a person. He was only a butterfly. Suddenly, he awoke and
found himself laying there, a person once again. But then he thought to
himself, "Was I before a man who dreamt about being a butterfly, or am I
now a butterfly who dreams about being a man?"

From: http://www.cyjack.com/cognition/Zen%20Stories.htm