For people fascinated by animal behavior, otters have long been a source of curiosity. Their poop (called spraint) has a somewhat pleasant smell and can be used to communicate sex, age, and other information to other otters who take a whiff. Female otters can “adopt” orphan otters as their own. And they can even use tools, wielding rocks to smash open food like clams.

Now, scientists are trying to decipher why these cute creatures are so fond of a peculiar pastime. They like to juggle pebbles.

In a study published in the Royal Society Open Alliance journal, researchers at the University of Exeter took a closer look at 48 otters scattered across three wildlife parks and zoos in the UK. Two species, the Asian small-clawed otter (Aonyx cinerea) and the smooth-coated otter (Lutrogale perspicillata), were involved. The otters were observed lazing around on their backs, tossing pebbles around. (For an otter, “juggling” means moving a stone around their chest, hands, and mouth.) While clearly adorable, the question for scientists was whether this was a form of play or a behavior tied to something else.

It could be an expression of hunger, as the otters tended to juggle more when they hadn’t eaten for two or more hours—the otter version of banging silverware on the table. It’s also possible the otters were playing with the rocks because it mimics the effort of foraging. The Asian small-clawed otter uses dexterity to find shellfish, while the smooth-coated otter eats fish. Both were observed to juggle, however. And after being given food in containers that needed to be tampered with, it didn’t appear that the otters were using the same skills exhibited in the rock-tossing.

It’s possible the otters are driven to juggle instinctively to help develop necessary motor skills early in life and to stave off cognitive decline later in life. (Both younger and older otters were observed to engage in the practice.)

Another explanation: otters get fidgety and bored and want something to do. Further research is needed to tease out why these playful creatures behave the way they do.

[h/t The Guardian]