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.
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“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.”