I have learned what a rat king is and now must tell you that “the strange expression ‘rat king’ is traditionally applied to a rare phenomenon—a group of rats whose tails are tied together.” This definition comes from the article “Rat kings in Estonia” which includes this as its Figure 1:

Here’s the story behind this remarkable (is that the right word?) specimen:
On 16 January 2005 farmer Rein Kõiv discovered a huddle of squeaking rats on the sandy floor of his shed in Saru village, Mıniste parish, Vıru county, Estonia. The animals were unable to escape, and the farmerís son killed them with a stick. After that a cluster of 16 rats were excavated from the frozen sand. Their tails were tangled in a knot that contained frozen sand. At the time of discovery only about 9 of the rats were alive. Obviously the animals tried to dig themselves out of the narrow tunnel, and the first rats buried the last ones under the sand. The crater in the sandy floor could still be seen even two months later.
The farmer knew nothing about rat kings. Nevertheless, the find seemed curious and he put the rats on a pile of planks where neighbours and chance visitors could observe them. It was only about two months later that Mr. Evar Saar, a relative of the farmer’s wife and a local reporter, ran across the animals and asked zoologists for comments. After that an avalanche of reports followed in Estonian journals and newspapers, and on the radio and television.
I can’t say I recommend reading the Wikipedia page for Rat king. It has all these upsetting passages where the term rat king is used as if it were a discrete thing that is either “alive” or “dead” rather than a collective made up of discrete beings. For instance:
On 20 October 2021, a live rat king of 13 rats was found in Põlvamaa, Estonia. The rat king was taken to Tartu University and euthanized due to the rats having no way of freeing themselves. Before that, scientists were able to film the rat king alive.
This term/phenomenon struck some extra fear into me because as soon as I read it, I half-remembered using the phrase “rat king moves” in one of my stories, to describe a character’s climbing a fence. Reader, I had not meant this kind of rat king. I just meant, you know, in the manner of the king of the rats!
I just went back and checked the story, and I’m happy to report that the term I used was slightly, crucially, different.
I climb three-quarters up the chain-link, king rat moves, but then I grab some barbed wire by the barb. Bleeding, cold, I clink back down. Suck on my palm.