Normally the sight of a crocodile swimming up to you would be a reason to scream and run.

But what if the crocodile just wanted a belly rub? Or to play catch?

Yes, it seems that crocodiles and related species—best known for their sharp teeth and underwater death rolls—have a playful side. A paper published this month in the journal Animal Behavior and Cognition reveals that crocodiles, alligators, and caimans have been known to engage in activity that appears to have no purpose other than to have fun.

Among the playful activities cataloged in the paper: surfing waves, playing with balls, sliding down inclines, giving each other piggyback rides, and carrying flowers in their mouths.

Sometimes the crocs engaged in solo activity. Other times they involved other crocodiles in their play. Once in a while they even engaged other species in their games. The paper’s author, University of Tennessee psychology professor Vladimir Dinets, even documented an alligator playing with a bunch of river otters. The otters started out teasing the alligator, but it responded by pulling one of the otters underwater and then repeatedly letting it go.

This might seem like terrifying behavior, but Dinets observed it several days in a row, so both species were obviously into the whole thing. There’s no word on who was keeping score, however.

Dinets said that he wasn’t the only person to observe this activity; he was just the first to take the playful behavior seriously. “Well, a lot of people knew about play in crocodilians, but there was almost nothing in scientific literature,” he said. “So I decided to fill the gap.”

Dinets has spent more than 3,000 hours in the field studying crocodilian behavior, but that alone wasn’t enough for a full scientific paper. To compile more information, he attended conferences and turned to several croc-related Facebook groups where other people could report the behavior they had seen.

He wasn’t flooded with responses—he only got a handful—but it was enough to show that crocodilian species play around with the movement of water (surfing waves, for example), interact with floating objects (such as balls or vegetation), and engage in social play (such as two juveniles swimming around each other in circles).

Most of these admittedly rare activities were observed in captivity rather than in the wild. That could suggest the crocs in zoos are less stressed than wild animals. “Either that or it's just easier to observe play in captivity, and a lot of people are watching their captive animals,” Dinets said.

Even if the behavior is more common in captive animals, that’s important to know because hundreds of thousands of crocodilians live on farms and zoos and keeping them properly engaged with playful activities may help to reduce stress and make them healthier.

Dinets said studying play is also important work toward understanding human and animal brains and behavior.

“Play is an important window into the works of the brain, but we are only beginning to figure out how to use it,” he noted. “For example, it is increasingly clear that play is generally more common in animals with complex, flexible behavior and that the tendency to play has evolved independently many times. Why does it happen, we don't know.”

Although he started the research, Dinets is moving on to other topics. He hopes future researchers will take up his mantle and try to study differences between wild and captive play, or examine whether juveniles engage in more play than adults, as is common with other species.

Of course, if you see a crocodile or an alligator in the wild, it’s probably best if you don’t try to play with it. But if you have a video camera with you and you see some crocs playing with one another, well then, YouTube is waiting.