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Go to Brilliant.org/SciShow to learn more. [♪ INTRO]. If you give a pile of fresh horse poop to a panda… well, it’ll probably give you a funny look.

Unless it’s cold out, that is. If it’s chilly enough, the panda might start to roll around in the poop and smear it all over itself. It’s not because the poop is warm… but it does help pandas manage chilly temperatures in another way.

Over the course of about ten years, Chinese researchers studying the behavior of wild giant pandas noticed this weird poop-bathing behavior. It seemed to be specific to horse poop. The scientists described the pandas as smearing horse manure over their entire bodies.

Now, this raises an obvious question: Uh, why?  Well, the  inevitable march of science being what it is, researchers decided to find out. And in 2020, they reported that they’d finally solved the mystery. Their observations showed a strong connection with temperature.

Basically, pandas only do this when temperatures drop below 15 degrees. That provided one clue: the poop-smearing habit had something to do with the cold. A second clue was that the poop generally had to be less than 10 days old for it to be appealing to the pandas.

It did not have to be steaming hot. Just relatively fresh. That gave the scientists the hint they needed to start looking at volatile compounds.

These are chemicals that waft into the air and are often responsible for scents. In this case, the smell of horse poop. Their search eventually led them to two chemical compounds, beta-caryophyllene and caryophyllene oxide.

These are members of a group of chemicals called terpenes, which are often found in plants.   Beta-caryophyllene is what gives pepper its pepperiness, and caryophyllene oxide is found in plants like lemon balm and eucalyptus.   I know, that’s probably not what you imagine when you think of the smell of horse poop. But these compounds were wafting abundantly from the relatively fresh poop that the pandas preferred. Older manure had less of them.   And when the researchers tried sprinkling these compounds on hay and giving it to zoo pandas, they rolled around in it, just like their wild cousins did with the poop!   So what’s the deal?

Well, it turns out that these chemicals mess with our bodies’ cold sensors.   In the study, the researchers demonstrated that mice given the compounds were less sensitive to the cold.   Plus, they discovered that these compounds inhibit pandas’ TRPM8 receptors, the major player in how our bodies sense cold. These proteins react to temperature and let your brain know that you’re coming into contact with something cold. But there are ways of tricking these receptors.

Menthol activates them, for example, which is why mints can make your mouth feel cool. And it turns out that the terpenes in fresh horse poop have the opposite effect, keeping pandas’ TRPM8 receptors from working properly. So basically, by rolling in horse poop, the pandas are probably dulling the sting of the cold.

It almost makes you wonder why other animals haven’t discovered the wondrous warming powers of horse manure. Then again…maybe they’re just sensible enough to look for other ways to stay warm. And now, because every sponsor wants to be mentioned in the same breath as poop, let’s talk about Brilliant.

Brilliant’s daily challenges will help you get just that little bit smarter on the regular, and practice the reasoning skills that scientists needed when they asked whether pandas might have a good reason for rolling in dung. Each challenge also ties into a whole interactive course if you want to learn more. You can get started at brilliant.org/scishow, with the chance to save 20% on an annual premium subscription.

And thank you for your support! [♪ OUTRO].