He's picking up all sorts of information by sniffing the grass.
It's no surprise that you don't see law enforcement agencies using humans for drug sniffing and similar activities. Dogs have a much better sense of smell than people. Estimates vary, but the typical dog's nose is between 10,000 and 100,000 times more sensitive than the human's.
Olfactory Receptors
Humans possess two receptors to detect smell, consisting of approximately 5 million to 6 millions cells. Our olfactory receptors are located in our upper nasal passages. The average dog's olfactory receptors contain about 220 million cells. They have an additional olfactory receptor known as the vomeronasal organ, two sacs opening into either the nose or mouth, according to the Alabama Cooperative Extension. Just as some people have a keener sense of smell than others, so do certain canines. As people age, their sense of smell declines, as do other senses, such as seeing and hearing. That's also true of dogs.
The Canine Nose
The dog's olfactory aptitude is 10,000 percent to 100,000 percent greater than the human's. The area of a dog's brain devoted to smell analysis is approximately 40 times the size of ours. While smelling and breathing goes through the same system for us, in dogs there's a separate path for air and odors. When we breathe out, the air leaves the same way it entered. In dogs, approximately 12 percent of inhaled air heads into the vomeronasal organ. Exhaled air leaves through small openings in the sides of the nose, rather than the nostrils. That also means a dog can sniff during both inhalation and exhalation processes, a feat humans can't.
Segregating Smells
When you start cooking dinner, it's likely Fido gets up from wherever he's been resting and hangs out in the kitchen. If you're putting a stew together, you can smell the beef and onions while its heating, but your dog can make out every single ingredient in the pot. That same process allows drugs trained to detect drugs or track people to focus on that particular scent, no matter what other odors surround it.
Breed Differences
Dog breeds all result from humans breeding canines through generations to acquire specific traits. Dogs bred primarily for tracking game, rather than herding or guarding, generally have better senses of smell than other canines. These breeds include the bloodhound -- the classic tracking dog -- the beagle and the basset hound. Brachycephalic breeds, those with pushed-in faces with short noses, literally don't have as many cells to detect odors on their noses. These breeds include the pug, the bulldog, the Pekingese and the Boston terrier.
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