Dr. Vint Virga likes to arrive at a zoo several hours before it opens, when the sun is still in the trees and the lanes are quiet and the trash cans empty. Many of the animals haven’t yet slipped into their afternoon ma­laise, when they retreat, appearing to wait out the heat and the visitors and not do much of anything. Virga likes to creep to the edge of their enclosures and watch. He chooses a spot and tries not to vary it, he says, “to give the animals a sense of control.” Sometimes he watches an animal for hours, hardly moving. That’s because what to an average zoo visitor looks like frolicking or restlessness or even boredom looks to Virga like a lot more — looks, in fact, like a veritable Russian novel of truculence, joy, sociability, horniness, ire, protectiveness, deference, melancholy and even humor.

The ability to interpret animal behavior, Virga says, is a function of temperament, curiosity and, mostly, decades of practice. It is not, it turns out, especially easy. Do you know what it means when an elephant lowers her head and folds her trunk underneath it? Or when a zebra wuffles, softly blowing air between her lips; or when a colobus monkey snuffles, sounding a little like a hog rooting in the mud; or when a red fox screams, sounding disconcertingly like an infant; or when red fox kits chatter at one another; or when an African wild dog licks and nibbles at the lips of another; or when a California sea lion resting on the water’s surface stretches a fore flipper and one or both rear flippers in the air, like a synchronized swimmer; or when a hippopotamus “dung showers” by defecating while rapidly flapping its tail?

Virga knows, because it is his job to know. He is a behaviorist, and what he does, expressed plainly, is see into the inner lives of animals. The profession is an odd one: It is largely unregulated, and declaring that you are an expert is sometimes enough to be taken for one. Most behaviorists are former animal trainers; some come from other fields entirely. Virga happens to be a veterinarian, very likely the only one in the country whose full-time job is tending to the psychological welfare of animals in captivity. He works with zoos across the United States and in Europe, and like most mental-health professionals, he believes that his patients possess unique personalities and vibrant emotional lives. His recent book is titled “The Soul of All Living Creatures.” What all of this means is that Virga, a man trained in the scientific method, has embraced notions that until recently were viewed in the scientific community as at best controversial, and at worst nonsense.

The notion that animals think and feel may be rampant among pet owners, but it makes all kinds of scientific types uncomfortable. “If you ask my colleagues whether animals have emotions and thoughts,” says Philip Low, a prominent computational neuroscientist, “many will drop their voices to a whisper or simply change the subject. They don’t want to touch it.” Jaak Panksepp, a professor at Washington State University, has studied the emotional responses of rats. “Once, not very long ago,” he said, “you couldn’t even talk about these things with colleagues.”