"Life on the Edge - Chapter 5" explores the sense of smell in various animals, starting with anemonefish and salmon. It examines how animals navigate using smell, discussing the olfactory capabilities of dogs and other creatures. The chapter then investigates the complex mechanisms behind olfaction, including the shape theory and vibration theory, and the research of scientists like Richard Axel and Linda Buck, who won the Nobel Prize for their work on odor receptors. It presents research into how flies and humans distinguish between normal and deuterated compounds and introduces a hypothesis of how olfactory receptors work in a similar way to a swipe-card machine. Ultimately, the chapter highlights the ongoing scientific quest to understand the structure of olfactory receptors and the quantum mechanical mechanisms involved in smell.