How Dogs ‘Hear’ Through Smell

Dogs lead with their nose — about 300 million scent receptors versus our roughly 500, and an olfactory membrane 30 times larger — so they read the world by smell, picking up fear and a racing heartbeat, telling a newcomer's age and origin at a sniff, and even alerting to epilepsy, blood-sugar swings, and cancers with over 90% accuracy. They also 'hear' our moods: the body-heat, heartbeat, and breath changes of an angry owner travel through the air and give the game away.