A shaggy brown terrier approaches a large chocolate Labrador in a city park. When the terrier gets close, he adopts a yogalike pose and crouched on his forepaws while hiking his butt into the air. The Lab gives an excited bark, and soon the two dogs are somersaulting and tugging on each other's ears. Then the terrier takes off and the Lab gives chase, his tail wagging wildly. When the two meet once more, the whole thing begins again.






He began studying animal behavior in the early 1970s and spent four years videotaping groups of dogs, wolves and coyotes in large enclosures. After filming, he slowly played back the tapes to jot down every nip, yip and lick. "Twenty minutes of film could take a week to analyze," he says.

The data revealed insights into how the animals maintained their tight social bonds -- by grooming each other, for example. But what changed Bekoff's life was watching them play. The wolves would chase each other, run, jump and roll over for seemingly no other reason than to have fun.




Bekoff also spotted a number of other blink-and-you'd-miss-them behaviors, such as a sudden shift in the eyes, a squint that can mean "you're playing too rough," and a particular wag of the tail that says, "I'm open to be approached." Humping a playmate during a romp, meanwhile, was often an invitation to nearby dogs to come join the fun.



Even morality hints at something deeper, however. To enforce moral conduct, dogs must be able to experience a spectrum of emotions, from joy to indignation, guilt to jealousy. They must also be able to read these emotions in others, distinguishing accident from intent, honesty from deceit. And recent studies by other scientists have shown evidence of these abilities, confirming what many dog owners already felt about their pets.



Bekoff's recent work suggests another remarkable canine skill: the ability to know what another animal is thinking, or the so-called "theory of mind."

Dogs seem to display a rudimentary form of this skill during play. Bekoff has noticed, for example, that one dog won't begin trying to play with another dog until he has her attention. To get her to notice, he might nip the other dog or run into her field of view. That, Bekoff says, shows that the one wanting to play knows she's not paying attention to him. Though this might seem like a simple skill, it's incredibly important to our species. Without it, we can have a hard time learning or interacting with the world around us.


"Dogs have an amazing relationship with us, and Marc (Bekoff) has done a beautiful job helping us understand them," says Brian Hare, a biological anthropologist at Duke University and one of the world's foremost experts on canine cognition. "Play gives us a peek inside their heads and helps us understand how they became the species they are today."