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Vincent Janik,Apps Archives a marine biologist, vividly recalls watching a pod of dolphins play with seagrass during a field visit to Mikura Island in Japan in 2014. 

"They were wrapping the seagrass over their fins and flippers, and passed it on for other dolphins to pick up," Janik, who is also the director of the Scottish Ocean Institute in the United Kingdom, told Mashable.

Most animals, humans included, play. But play in dolphins and some other marine mammals seems especially remarkable. Dolphins are profoundly curious creatures, which drives them to seek activity and stimulation. What's more, the facial anatomy of a dolphin makes it look like they're smiling, and they perform notably playful acts like performing somersaults and leaping around boats.

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"Why do dolphins play?"might seem like a simple question. But it's hard to identify the reasons, say marine researchers. What looks like play to humans might be more than just fun to dolphins.

SEE ALSO: There's a fascinating new clue to the giant megalodon's extinction

Playing is not always what it seems

Sometimes the highest level of brain development in animals happens during play, and this could be the case for dolphins, Holli Eskelinen, a dolphin researcher and a lecturer at the University of Miami Rosenstiel School of Marine and Atmospheric Science, told Mashable. 

Eskelinen once observed a dolphin calf playing with a stick in its mouth. After a couple of months, she found the dolphin learned to use the same stick movement to manipulate and move mangrove seed pods. So, as the dolphins grow, play becomes a way for them to learn what they're capable of, and to stimulate their brains.

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"What we observe might be anecdotally classified as play, but it could serve a bigger biological purpose," Eskelinen told Mashable.  

"What we observe might be anecdotally classified as play, but it could serve a bigger biological purpose."

Though play is a behavior associated with many terrestrial and aquatic creatures, it is dolphins’ curious nature that possibly separates their play behavior from that of other animals, according to Janik. For instance, dolphins become intrigued when they encounter puffer fish, an interesting creature that blows itself up like a ball to evade predators. But dolphins chase these fish, and sometimes play catch by passing them back and forth.

A BBC documentaryeven claimed that a toxin released by puffer fish intoxicates dolphins. However, that's still a hypothesis. There isn’t nearly enough evidence to prove the intoxication theory, according to Heather Hill, who researches dolphin behavior and teaches psychology at St. Mary’s University, in Texas. "I think puffers are just another kind of interesting thing for dolphins to mess with," she said.

For dolphins, play starts young. By playing, dolphin calves learn to interact with other members of their pod. It helps them understandthe emotional state of other dolphins. They begin playing just days after birth, when mothers nurse their young. This, surprisingly, often involves the genitalia, explained Hill. The mother, with its rostrum or mouth, basically gooses its calves. The calves appear to find that pleasurable, Hill said.

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Dolphins in captivity get more opportunities to play because they don't have to spend time foraging. Credit: Checchi Alberto / Getty Images

In captive conditions, such as zoos, there are many opportunities to watch dolphins flip and play with objects. Dolphins, being social mammals, get along well with humans in these environments, said Hill. "We can often get them to play hide and seek and peekaboo kinds of games," she said. Wild dolphins, though they don't have the same toys, have similar play behaviors. But these free dolphins must spend more time foraging and hunting, meaning they have less time to play. 

Dolphins become curious when they encounter puffer fish, a fish that inflates itself to escape from its predators. Credit: Ramil dolphins / Shutterstock

Sometimes dolphins, be it captive or wild, do seem to play just to have fun and perhaps relax, said the Scottish Ocean Institute’s Janik. Dolphins play an unusual game, creating bubble rings in the water that last for about a minute. They do this by exhaling air near the water surface. Then, they destroy those bubbles by biting or just swimming through them.

"There's a lot of questions that still need to be answered and connected for us to understand."

But, it becomes a bit tricky to distinguish between a play fight and serious fight in dolphins, Janik explained. The physical behaviors that we see in play can also be seen when dolphins clash, or when they become aggressive. In some animals, like in dogs or wolves, it's very clear when the animals are sending non-serious play signals, Janik said. "But this is not the case with most marine mammals," he told Mashable.

Overall, there's still much to learn about dolphin play and overall behavior, emphasized Eskelinen. She remembers once watching a mother swimming around its dead calf for a period of time, and wonders what purpose it could have served. "There's a lot of questions that still need to be answered and connected for us to understand," Eskelinen said.