From Beverly Cleary’s Ralph S. Mouse to Stuart Little by E.B. White, the idea of adorable, heroic rodents doing miniaturized versions of human things has enthralled generations of kids. And then you have Mrs. Frisby and the Rats of NIMH, which should actually be classified as a horror story.

Robert C. O’Brien, a journalist for National Geographic, was inspired to write the 1971 tale about Mrs. Frisby’s quest after reading a study conducted by behavioral sciences researcher John Calhoun.

Dr. Calhoun spent the better part of a 40-year career working at the National Institute of Mental Health, or NIMH, conducting various experiments and studies on mice to see what would happen when their population grew too big for their environment.

His most famous experiment placed four pairs of mice into a mouse universe he called “Universe 25,” a 9-foot-by-9-foot metal pen with tunnels, nesting boxes, and food and water dispensers. The population doubled every couple of months, until it reached 620 mice on day 315. By day 560, there were 2,200 mice crammed into that 9x9 space—and things got pretty ugly.

Yoichi R Okamoto, WikimediaCommons // Public Domain

Mother mice kicked their babies out of the nest before the young were ready. Other mice wounded and killed the babies. Males lost the ability to protect their females. Fighting and cannibalism broke out amongst non-dominant males. Dominant males retreated into themselves, preferring to spend their time eating, drinking, and grooming. Calhoun called these guys “the Beautiful Ones.” Eventually, the mice stopped reproducing entirely, and the mouse society came to an end.

Now, here’s the scary part. Calhoun believed that the results of his studies on mice overpopulation directly predicted what would eventually happen with humans. He starts his paper with this:

“I shall largely speak of mice, but my thoughts are on man, on healing, on life and its evolution. Threatening life and evolution are the two deaths, death of the spirit and death of the body. Evolution, in terms of ancient wisdom, is the acquisition of access to the tree of life. This takes us back to the white first horse of the Apocalypse which with its rider set out to conquer the forces that threaten the spirit with death.”

So ... think about that the next time you break out Mrs. Frisby for a bedtime story.