All animals play. Running, rolling and wrestling with each other is a way for them to have fun, of course. But it also seems to be how they communicate and strengthen bonds with each other.

When a dog comes up to another dog, front legs bowed and his tail high and wagging, his buddy knows he wants to play. But new research shows that this play behavior is surprisingly similar when horses and dogs play.

"Up to now, most studies have focused on dog-human play due to the important implications such studies have in understanding the peculiar relationship we establish with our pets," researchers from Italy wrote in the journal Behavioural Processes. "Here, we focused on social play between dogs and horses."

To study interspecies communication, Elisabetta Palagi and her colleagues from the University of Pisa found 20 YouTube videos of dogs and horses playing where their interactions lasted at least 30 seconds. They analyzed the videos, looking for specific patterns of play.

They found that while playing, both dogs and horses often had relaxed, open mouths — which is a common playful facial expression in mammals. Some also copied each others' movements, like pretending to bite, playing with an object, or rolling on their backs on the ground.

The team also found that the dogs and horses mimicked each others' facial expressions. This behavior — called rapid facial mimicry — has been seen before in dogs, primates, meerkats and sun bears, points out National Geographic. But it has never been documented between animals of different species.

"Taken together, our results suggest that, despite the difference in size, the phylogenetic distance, and differences in the behavioral repertoire, dogs and horses are able to fine-tune their actions thus reducing the probability of misunderstanding and escalating into aggression."

Why communication matters

A 2,000-pound horse can frolic with a relatively tiny dog because the two are able to communicate their intentions.

"It's an important study because it shows how two animals who look and behave so differently can nevertheless manage to negotiate how to play in a way that's comfortable for both," Barbara Smuts, a behavioral ecologist at the University of Michigan, told National Geographic.

"It's even more noteworthy given the large size difference between horses and dogs. The dog is vulnerable to injury by the horse, and the horse has a deeply ingrained tendency to fear animals who resemble wolves."

Next up, the researchers write, is exploring the role of developmental pathways and familiarity in shaping Interspecies communication that "can be at the basis of a universal language of play."

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

Horses and dogs share universal play language
Despite their size difference, horses and dogs understand and mimic each other when they play.