The idea of a bunch of rats linking up to form some kind of grotesque rodent version of Voltron sounds like the stuff of fairy tales, but it turns out Rat Kings are real- and they're horrifying to behold too.
Rat kings are created when a bunch of rats end up with their tails so entangled they can't pull them apart, causing this cluster of rats to go in to full blown freak out mode.
Rat king sightings have been limited mostly to Germany, where they were seen as far back as the 16th century, and their existence is hotly debated by zoologists, who believe preserved rat kings are nothing but hoaxes.
And yet there have been too many sightings for rat kings to be nothing but a myth, and all the more recent squirrel king sightings have proven the theory of tail entanglement to be true.
So the real question is- how do the tails become entangled so tightly?:
The most plausible explanation is that black rats—which have long, supple tails and reside in close quarters during winter—may come in contact with a sticky or frozen substance such as sebum (secreted from the critters’ skin), sap, food, feces, frozen urine, or frozen blood. The bonding agent may solidify as the animals slumber. Once the rodents realize their tails are glued, they might create a tighter knot as they attempt to wriggle free.
This explanation has a ring of truth: Most rat kings were discovered during the winter or a frosty shoulder season, and they’re usually found in a tight shelter.
Read more from An (Almost) Comprehensive History Of Rat Kings at Mental Floss