Flavor is 80 percent smell and 20 percent taste. So does that mean dogs—which can pick up levels of TNT as small as a few parts per trillion, detect evidence of cancer in human urine, and sniff out the presence of health-threatening molds—have a better sense of taste than we do? And if they do, then why are they feasting on dirty socks? The answer to the question of what, exactly, dogs taste is not a simple one.

Dr. Katherine Houpt, a professor at the Cornell University College of Veterinary Medicine, has done some of the most extensive research to date on dogs’ palates. In her experiments, Houpt places different foods in front of a group of dogs and notes which bowl they eat from first, and how often they continue to eat when it’s refilled.

Contrary to their reputation, dogs, Houpt found, are discriminating eaters. They like meat above all else, and seem to prefer beef to pork, pork to lamb, and lamb to chicken. Last on their list is horsemeat.

They also appreciate a little novelty. “Despite their liking for a basic beef diet, variety is important,” says Houpt. Dogs will eat carrots, blueberries, and peanut butter, and appear to enjoy star anise, rosemary, tarragon, and oregano. But they’ll eat them for only a week before tiring of them. They altogether avoid spicier things like cinnamon and chili pepper.

Developing foods that appeal to a dog’s palate is big business —$14.7 billion was spent last year on pet food in the United States. Most of the big pet food companies conduct their own experiments and doggie focus groups, the results of which are trade secrets in a competitive industry. But to be truly successful, new products must appeal not just to dogs, but also to their human owners. The two species are often at odds when it comes to dog food.

Dogs, for instance, love the aroma and “silky mouthfeel” of fat, says Gerry Nash, owner of pet food producer Animal Food Services. “And they prefer moist food.” Nevertheless, approximately 80 percent of dog owners buy dry dog food, made mostly of grain, which is cheaper, lasts longer, and is less messy and smelly. So to try to reach a compromise, most pet food manufacturers spray their dry kibble with emulsified fats and smoky meat flavorings.

But what about the other doggy choices —the ones that turn our stomachs? While dogs have more than 200 million scent receptors, compared with our 5 million, they have far fewer taste buds. They have one-sixth of the 6,000 that humans have. And if having a large number of taste buds means greater sensitivity (human “supertasters,” for example, have up to twice as many numerous, densely packed receptors, which makes them far more likely to be picky eaters), this might be the reason why dogs eat trash.

On the other hand, humans also eat a lot of things that smell bad, notes Bruce Halpern, a researcher in chemosensory perception at Cornell University. And they smell bad because they are, in fact, rotting. Think Limburger cheese, nam pla (Thai fish sauce), and dry-aged beef.

One of the things that aging meat, other proteins, and foods that are rotting (or fermenting —a process of decay) have in common is a high level of glutamic acid, which both people and dogs experience as umami (a Japanese word for one of our five basic tastes, meaning meaty). Glutamic acid, which is naturally occurring, is most familiar to us in the form of the flavor enhancer monosodium glutamate, or MSG. As it turns out, dogs may be enjoying a savoriness in rotting garbage or dirty gym socks that, Halpern says, is “really not so different from what we consume.”

See more articles