When it comes to crime solving, the bloodhound is such a pro its evidence is admissible in U.S. courts. Classified as a scent hound — as opposed to a sight hound, a fast dog that tracks prey visually—the bloodhound has a uniquely powerful NOSE that’s been put to use trailing missing people and criminals for centuries.
Its olfactory membrane is, by some estimates, 40 times as large as a human’s. Its loose facial skin, including the pendulous FLEWS and DEWLAP, droopy ears, and abundant slobber all help a hound “hoover up” odor molecules, says Lisa Harvey, a biologist at Victor Valley College in California. Veteran hounds can track a person’s two-day-old scent through crowds, wind, and rain. But they can be stumped.
“They can’t always tell the difference between identical twins,” says Harvey, whose research suggests that the dogs may be sniffing something related to a person’s genetics. A human scent, says National Police Bloodhound Association President Doug Lowry, “is like a fingerprint to them.”