How can sharks smell blood from more than a mile away? — Fisher, Collinsville, Miss.
Humans don't have a particularly good sense of smell, and lots of animals blow us away in this department. Dogs, for example, can smell more things and are much more sensitive to smells in lower concentrations. A human has a "smell patch" the size of a postage stamp. A dog's is the size of a dinner plate. A shark's is even bigger. For more information, see How Sharks Work.