Two men were walking down a busy city street. “Listen,” exclaimed one. “What a lovely sound of a cricket.” The other looked at him in puzzlement. “How can you hear a cricket amid this din?” he asked. The first man replied, “I’m a zoologist.” He took a coin from his pocket and dropped it on the crowed sidewalk. Immediately, the people around stopped and began to look down. “We hear what we listen for,” he explained.