When people make ineffectual attempts to pronounce "NIMH" it's often in reference to Don Bluth's The Secret of NIMH. Famous for traumatizing children, the cartoon features a widowed field mouse who tries to save her sick mouse kid by getting help from a society of big-brained rats who dream of no longer having to eat garbage for sustenance. Why are the rats so smart? Because they escaped from the National Institute of Mental Health, or NIMH for short, where they were the test subjects of intelligence boosting experiments. Good news everybody, NIMH was a real place and their rat experiments were way darker than the book, movie or your nightmares depicted!
Albeit a bit lower on the terrifying special effects.
The author, Robert C. O'Brien, was inspired to write Mrs. Frisby and the Rats of NIMH after seeing the work of John B. Calhoun. Calhoun had an idea: that human society breaks down when we get too crowded. To test his theory, he introduced eight mice into something called the "Mouse Universe," an enclosed space with no predators, plenty of food and water, no disease, no bad weather and no hope for escape. The mice doubled in numbers every 55 days until there were about 600 of them.
And this was when things got weird.
Yoichi R. Okamoto
According to Calhoun, the males who failed in finding their niche in the Mouse Thunderdome listlessly hovered in groups in the middle of the floor and picked half hearted fights with each other. Males who couldn't find private space attacked females who were trying to nurse their litters, who then got mad and fought back or turned on their own kids. As time passed, sex drive decreased and the moms abandoned their litters or just straight up ate them. And then the mice stopped having sex altogether and started dying off. They weren't even overcrowded anymore, they just lost interest in being alive.
Robert C. O'Brien saw Calhoun's Mouse Hell and asked "What if one of those original eight mice escaped from his dystopia of asexual, angry baby-eaters? And what if he freed some superintelligent rats on his way out? WHAT WOULD THAT LOOK LIKE AS A CHILDREN'S BOOK?"
From that nugget of an inspiration, O'Brien wrote Mrs. Frisby and the Rats of NIMH, which was adapted into the cartoon The Secret of NIMH, which is now in development as a live-action, CGI movie. So...the rats will be real, this time guys.