Dogs play by chasing, tackling and nipping at each other, but there’s more to their lively antics than meets the eye. The way dogs interact with one another reveals that dogs have a language as well as a moral code, and they don't engage in play simply to establish dominance.

Marc Bekoff, professor emeritus at the University of Colorado at Boulder, has been studying animal behavior for more than 40 years. After reviewing four years' worth of footage of dogs, wolves and coyotes, he discovered that even dogs’ wild relatives play by chasing each other, rolling over and jumping on one another.

“Play is a major expenditure of energy, and it can be dangerous,” Bekoff told The Washington Post. “You can twist a shoulder or break a leg, and it can increase your chances of being preyed upon. So why do they do it? It has to feel good.”

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Bekoff and other researchers have conducted numerous studies on how these animals play and what their actions mean. What they’ve found is that dogs’ behavior during play is a language all its own, and every shift of the eyes or wag of the tail is a form of communication.

Play even has a set of rules, and if a dog breaks them — by playing too rough, for example — that dog may be excluded from group play. Bekoff says this response suggests that dogs enforce moral conduct, which means they’re capable of experiencing a range of emotions and even of recognizing these emotions in other canines.

What exactly do their different play behaviors mean?

dog doing play bowThe bow is a signal for play to commence — but there's more to it than that. (Photo: Mike McCune/flickr)

Play bow

When a dog lowers the front of its body in a bow-like stance, this is an invitation to play. If your dog often bows to other canines you meet while out on a walk, it’s a good indication that your pup would like a playmate.

However, this stance doesn’t only invite play. It also communicates to other dogs that the jump, nip or roughhousing that follows the bow isn’t an act of aggression. It’s simply a dog’s way of saying, “I’m just playing around.”

dog rolled over on grass while playingSee my belly? That has meaning too. (Photo: Eric Sonstroem/flickr)

Rolling over

When a dog rolls over onto its back during play, it’s often considered a submissive gesture; however, research suggests it could mean something else entirely.

Earlier this year, scientists at the University of Lethbridge and the University of South Africa observed 33 play sessions between two dogs, and they also studied 20 YouTube videos of dogs playing together.

While not all the dogs rolled over during play, those that did weren’t necessarily the smaller or weaker of the two dogs, nor were the dogs that rolled over exhibiting submissive behaviors such as decreasing play.

In fact, smaller dogs were no more likely to roll over than larger ones, and the pups that did roll over used the position to evade a nip or to get into position to playfully bite the other dog.

The researchers found that none of the 248 rollovers were submissive during play and concluded that rolling over is actually meant to facilitate play.

two puppies playfully wrestlingThere's a lot of communication going on here — though to human watchers it may simply induce giggles. (Photo: WilleeCole Photography/Shutterstock)

Letting female puppies win

A 2008 study found that male puppies frequently let their female puppy playmates win during play, even when the males were bigger and stronger.

The male dogs would even put themselves in positions that left them vulnerable to attack. For example, the male puppies would occasionally lick their playmates’ muzzles, which provided the female puppies with an opportunity to easily bite in return.

Why? Researchers say the act of playing may be more important to the male dogs than winning.

"Perhaps males use self-handicapping with females in order to learn more about them and to form close relationships with them — relationships that might later help males to secure future mating opportunities,” Camille Ward, lead author of the study, told NBC News.