Beagles aren't the best sniffers of all, but they're in the top three. Bassets may scent just as well as beagles, but they lack the beagle's drive. Bloodhounds may scent a little better, but they're big and slobbery. The trim, tidy beagle is probably the world's most popular scent hound.
The beagle's muzzle is big for his size, broad and deep, and flanked by floppy ears that stir up the air and flexible flews (upper lips) to help carry scent particles to the nose. It's big on the inside, too, packed with some 225 million scent receptors -- same as the much bigger and scarier German shepherd dog.
Once described as "a nose with feet," the beagle is a dedicated sniffer -- let him settle on a scent and he's hard to distract. He'll follow it uphill and down dale and out into traffic. Unless he's on a leash, he develops selective hearing and will just ignore you as he disappears over the horizon. Schnoz to the ground, he'll stay on the trail until it disappears or he comes up to the source, when he will bay to say, "I found it!"
He's not too big -- a beagle weighs around 30 pounds -- and he's cute and friendly, so he gets to go places that bigger and more intimidating sniffers can't go without upsetting folks. He can walk around an airport, making friends and being snoopy, while checking out everybody's carry-on bags for bombs or dope or contraband sausage. If he finds what he's looking for, he's polite -- he lets his handler know it's there by just sitting down.
The beagle's nose is highly discriminating -- he can be trained to recognize and follow almost any scent to the exclusion of all others. If you're checking incoming airplanes for hitchhiking brown tree snakes invading the United States, he'll ignore oil, jet fuel or other airplane-related scents. If you're checking a house for termites or bed bugs, that's what he'll cue on, not the Cheerios that the baby dropped. He's not just a one-trick pony, either -- a well-trained working beagle can recognize as many as 50 different scents.