Thanks to Brilliant for supporting this episode of SciShow.

Go to Brilliant.org/SciShow to check out their course on number theory. [♪ INTRO]. Raccoons are famous for their habit of dipping and shaking their food in water before eating it.

This behavior is called dousing, and it looks a lot like they're washing their food. For a long time, scientists thought that's exactly what it was… but there's good reason to think that's not what they're up to. For one thing, they only do it in captivity.

You might see a wild raccoon with its hands in the water, but they're not washing food, they're looking for it. Raccoons' front paws are very dextrous and very sensitive, and they're the animal's main tools for foraging. On land or in water, raccoons use patting motions to feel around for treats, investigating whatever they find with their hands before putting it in their mouths.

But captive raccoons will actually carry food to water, dip it in and move it around, and then pick it up and eat it. One of the most famous and often-referenced studies to explore this behavior is a series of experiments from 1963 that presented food to captive raccoons in various scenarios. Most notably, the raccoons were no more likely to douse muddy food than clean food.

Which is a strike against them being neat freaks. There was also the hypothesis that they were moistening their food to help it go down easier. But raccoons had no preference for dousing dry food over the wet stuff.

One hypothesis still in the running today is that water makes those already sensitive paws super-powered. The 1963 study partially tested this: based on evidence that warmer water increases sensitivity, they ran trials with one raccoon to see if it had a preferred dousing temperature… which it didn't. But more recent research has found that wetting a raccoon's hands makes the nerves in the skin much more sensitive.

So it might be that dousing helps raccoons get a better feel for their food. But that 1963 study also supports a different explanation for dousing: that the raccoons just can't help it. The experiments revealed that raccoons doused more when a water dish was easily accessible, when the dish had sand in the bottom, and if the food was something aquatic like a shrimp or mussels.

These patterns lead some scientists to suspect this behavior might be a fixed action pattern -- basically, an instinctual compulsion. Captive raccoons don't need to search in water for food. It's just kind of handed to them.

But if they find themselves holding aquatic prey and the nearby water dish has a sandy bottom like a stream, their brains might just be hardwired to go through the motions of their wild foraging behavior, even though they don't have to. This might be similar to the way cats in captivity will bat food around to simulate the feeling of hunting prey. So raccoons may not be little food-washers, but they are talented and specialized foragers who -- for one reason or another -- just can't help playing with their food.

If you want to play with something a little more sophisticated, you might be interested in the courses over on Brilliant. Like their course on number theory. It'll teach you everything you ever wanted to know about how numbers work -- from prime factors to infinity.

So… that's a lot! You can find this interactive course and many more in science, math, engineering, and computer science over on Brilliant. Right now, the first 200 people to sign up for an annual premium subscription at Brilliant.org/SciShow will get 20% off.

So check it out if you're interested! [♪ OUTRO].