Anyone who has bonded with a puppy madly sniffing with affection gets an idea of how scents, most not apparent to humans, are critical to a dog’s appreciation of her two-legged friends. Now new research suggests that humans also pick up infinitesimal scents that affect whether or not we like somebody. The smells elicited psychological and physiological changes suggesting that humans get much more information from barely perceptible scents than previously realized.