There’s nothing quite like the behavior of panicky humans—especially when it comes to hoarding. Let a blizzard approach or a hurricane churn toward shore, and we descend on stores, buying up more batteries, bottled water and canned foods than we could use in a lifetime. We’re seeing the same thing again as America hunkers down against the novel coronavirus, and of all of the products that are being snatched up the fastest, there’s one that’s in special demand: toilet paper.

The Washington Post reports a run on the rolls, with both Costco and the Giant supermarket chain stripped all but clean. Even Amazon’s physical stores “appeared to be down to single rolls of novelty toilet paper in some places Friday,” the Post said. The New York Times similarly reports from a Whole Foods supermarket in Somerville, Mass., where shoppers had to be limited to two packages of toilet paper each, lest they strip the store bare.

But why? What is it about toilet paper—specifically the prospect of an inadequate supply of it—that makes us so anxious? Some of the answer is obvious. Toilet paper has primal—even infantile—associations, connected with what is arguably the body’s least agreeable function in a way we’ve been taught from toddlerhood. Few, if any of us, remember a time when we weren’t acquainted with the product.

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“There is comfort in knowing that it’s there,” says psychologist Mary Alvord, Associate Professor of Psychiatry and Behavioral Sciences at the George Washington University School of Medicine. “We all eat and we all sleep and we all poop. It’s a basic need to take care of ourselves.”

We are also exceedingly social creatures, and we count on the community for our survival. People seen as unclean or unwell are at risk of being shunned—which in the state of nature could mean death. “We’ve gone beyond using leaves,” says Alvord. “It’s about being clean and presentable and social and not smelling bad.”

The coronavirus panic has only made things worse. We know exactly when hurricane or blizzard season is approaching, and stores and supply chains can prepare. No one foresaw the season of corona.

“We, as a country, responded slowly,” says psychologist Baruch Fischhoff, professor in the Department of Engineering and Public Policy at Carnegie Mellon University. “Until very recently, many people heard assurance that this was not a major problem. Then, suddenly, they were told to stock up, for an indeterminate period.”

When it comes to stocking up, different basics offer differing options. “If people did not find the food that they wanted, they could buy other food,” says Fischhoff. “For toilet paper, there are no substitutes.”

The need to hoard the one product for which there is no alternative is only exacerbated, he adds, by the fact that it is not clear when the possible shortages will end. America’s late-to-the-party response to the COVID-19 pandemic means shoppers have not been “given assurances that the supply chain issues would be managed in due course.”

They likely will be, just as the virus will be brought under control—eventually. Until then, humans will be humans and our eccentricities will be our eccentricities. Our panic buying, Alvord says, represents one thing we can control. In an exceedingly uncertain moment, it’s at least something.

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.