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For people, smiling is an easy way to avoid misunderstandings. And according to a new study, bottlenose dolphins may use a similar tactic when playing with each other.

The study, published Wednesday in the journal iScience, found that dolphins make an open-mouth expression similar to a “smile” during their play.

To conduct the research, a group of scientists from institutions in Italy and France observed 11 dolphins at Zoomarine Rome and another 11 at Planète Sauvage in western France as they played with each other, with their human trainers and on their own.

The researchers found that the marine mammals almost always “smiled” when they were in their playmate’s view, and that their playmate “smiled” a third of the time. This suggests it is a form of communication, they said, hypothesizing that by “smiling” at each other, the dolphins could prevent their games from turning into a real fight due to misunderstandings.

Although their facial expression resembles a smile to humans, dolphin communication expert Heather Hill, a professor of psychology at St. Mary’s University in San Antonio, Texas, who was not involved in the study, cautions against extrapolating too much.

“I think the dolphins react in game situations with their mouths open, and it…seems reasonable that this is a form of communication.” I don’t feel comfortable calling it a smile because it is the representation of the open mouth in many other contexts as well,” she told CNN, referring to its use in aggressive, solitary and playful actions.

“Should we really just interpret it as an open-mouthed exchange that takes place between two people to communicate, ‘Hey, we’re on the same page,'” she added. “…Does that necessarily mean that it’s fun because it’s a game, and that’s why you and I smile at each other like a human or a chimpanzee would… I’m not sure I’m ready to take the next step to do.”

Deeply loved – and humanized – by humans, dolphins are known for their playfulness, rich social lives and complex communication with one another. They have many different ways to play together, such as jumping, breaching or dashing across the water, slapping the surface of the water with their tails, playfully fighting, or surfing the waves.

But despite dolphins’ reputation for playfulness, their facial expressions while playing have never been studied before, although studies have shown that other mammals such as humans and monkeys communicate with an open mouth and a smile while playing. Scientists largely believe this behavior is due to a change in biting action without actual contact, the study says.

Researchers in the latest study found that 92% of the cases in which dolphins used the open-mouth expression occurred when they were playing with each other, rather than with humans or alone.

When dolphins engaged in an aggressive interaction or a more relaxing activity such as parallel swimming or swimming upside down, the scientists did not observe the “smiling” expression.

The researchers also noted the importance of the dolphins’ vocal communication during their play and said that this could be a focus for future studies since they did not record these signals.

“Dolphins have evolved one of the most complex vocal systems in the animal world, but sounds can also expose them to predators or eavesdroppers,” corresponding author Livio Favaro, a zoologist at the University of Turin, said in a statement.

“When dolphins play together, a mix of whistles and visual cues help them cooperate and achieve goals, a strategy that is particularly useful in social play when they are less wary of predators,” he added.

All dolphins observed for this study live in captivity. Hill noted that the “smiling” behavior likely occurs in the wild as well, but perhaps less frequently as they spend more time searching for food and avoiding predators.

“The next step would be to use the same methodology … work with these wild species and see what they do in the same context,” she said.