Man’s best friend loves to play, and there’s been extensive research into the rules of engagement between dogs. Mimicking signals let dogs know when their buddies want to goof around and it’s a behavior that’s been observed in species-specific play such as cats playing with cats. Now, for the first time, a study published in the journal Behavioural Process details how mimicking as a means of play engagement has been observed across species, as horses were shown to copy their canine friends.

Playing between humans and dogs has been the main interspecies play focus up until now, but researchers at the University of Pisa decided to examine how play occurred between horses and dogs. Looking at 20 videos of dog-horse social play, the team identified play behaviors that were exhibited by both species and those that were species-specific. They found that the playful tactics between the two species, such as mixing up movements and self-handicapping, were quite well balanced between the two animals.

A play technique called the Relaxed Open Mouth (shortened to ROM and incidentally how I’ve spent most of lockdown) is widespread among animals and essentially is defined by making funny facial expressions. The videos revealed that even horses practice it and to an equal extent as their play partners when engaged with dogs.

Another play technique called Rapid Facial Mimicry (RFM) is seen when animals quickly copy their play partners' expressions. It’s thought to act as a way of “mood sharing” during play. From the research, the team found that horses were more likely to copy their playmates' goofy expressions than mimic "play biting" behavior, though non-aggressive biting was still observed in both species.

The two techniques of play and communication came together to see the horses copying the open-mouthed expressions of the dogs, and mimicking movements and the mood of their play partner. The researchers claim that this demonstrates that dogs and horses do actively engage in play and mimicking behaviors, despite their significant differences in size and species. They also concluded that dogs and horses are able to fine-tune their actions when playing to reduce the risk of any crossed wires, which could turn it into a fight, and suggest that identifying a universal language of play that enables such interspecies interactions would make an interesting focus for future research.