All humans whether alive or deceased emit microscopic particles bearing human scent. A dog’s sense of smell is not only more powerful than ours, it is more discerning. Thus a dog can pick out a target odor in a sea of odors, especially if his concentration is reinforced by periodic exposure to an item of clothing or other object handled or worn by the person he is seeking. When trailing a person, a dog keys in on the odor of skin cells that flake off the body. Trailing dogs work on-lead. They follow the skin-cell trail wherever it leads, even though it is mixed with other scents.