Is it true that a shark can smell a drop of blood from a mile away?

No, but they can detect blood from very far away. Sharks are carnivores (meat eaters) known for their keen sense of smell. Sharks have two nostrils through which some species can detect odors up to almost 300 feet (91 meters) away, which is about the length of a football field. Fourteen percent of the Great White shark’s brain matter, for example, is devoted to smell. Sharks zig-zag along ocean currents, using their highly sensitive nostrils to find sources of odors and food. Some species can smell one molecule of blood in over one million molecules of water—which is equal to one drop of blood in 25 gallons (94 liters) of water. A shark can also detect vibrations of passing prey with its “lateral line,” a row of sensors along the side of its body.