Hosted by naturalist Diane Ackerman, this "Mystery of the Senses" installment of "Nova" examines the sense of smell. Ackerman tracks the human response to smell from the nose to the brain and looks at how different animals rely on their sense of smell. To gain a deeper understanding of how natural and manufactured smells affect our mood, Ackerman travels to the incense-intense country of Oman and visits a New Jersey perfume factory.