The Sisters of Plenitude are familiar to fans of BBC’s Doctor Who. The nuns lived on New Earth in New New York (technically, “New New New New New New New New New New New New New New New York,” because it was the fifteenth New York to have been established) in the year 5,000,000,029. They were known for their devotion to caring for the sick, and they could be recognized by their distinctive white habits.

In case that is not a good enough description, perhaps you could identify them by the fact that they are cat women.

No, we’re not talking about Catwoman, of Batman lore, nor are we talking about ladies who have a propensity for collecting stray cats. The Sisters of Plentitude were a peculiar blend of human and feline DNA that made them perfect characters for a television program centered around science fiction.

Leaving the realm of sci-fi behind, reality gives us something at least as interesting. Five hundred years ago, the inhabitants of this planet dealt with a curious and terrifying set of circumstances that appeared to create dangerous real-life cat nuns throughout Europe.

In his book Epidemics of the Middle Ages, Justus Friedrich Karl Hecker (1795-1850) makes an almost-casual observation about a curious affliction in the Middle Ages that seemed to be limited to nuns. He wrote, “I have read in a good medical work that a nun, in a very large convent in France, began to meow like a cat; shortly afterward, other nuns also meowed. At last, all the nuns meowed together every day at a certain time for several hours together. The whole surrounding Christian neighborhood heard, with equal chagrin and astonishment, this daily cat-concert, which did not cease until all the nuns were informed that a company of soldiers was placed by the police before the entrance of the convent and that they were provided with rods, and would continue whipping them until they promised not to meow anymore.”

This was not the only incident in which nuns were afflicted with peculiar behavior. Jerome Cardan, a 15th-century German physician, was summoned to a convent in response to a peculiar situation. One of the nuns was acting distinctly un-nunlike. She started biting her fellow nuns. Rather than turn the other cheek, they started biting back. The biting propensities spread throughout the nunnery. That was mystifying enough, but the phenomenon didn’t stop there. Dr. Cardan wrote, “The news of this infatuation among the nuns soon spread and it now passed convent to convent throughout a great part of Germany, principally Saxony, and it afterward visited the nunneries of Holland, and at last the nuns had biting mania even as far as Rome.”

What on earth was happening, and why were these godly women acting in such an ungodly manner? German theologian Johann Jacob Zimmermann (1642-1693) opined that the strange behavior was the result of the nuns being kept in relative solitude and, because they were women, the stress of their environment subjected them to “fantastic affection.”

Zimmerman’s chauvinistic views would undoubtedly get him more than a few bites and scratches today. Subsequent researchers have agreed that the stressors peculiar to the life of a nun were a contributing factor and that, perhaps, the lesser-valued role of women in that society was the straw that broke the camel’s back. That the outbreak of cat sounds came to an end upon a promise from the sisters suggests that it was, at minimum, a voluntary act of rebellion on their part.

Whatever the cause or the intent, the actions of the nuns caused consternation throughout Europe. As incidents spread from convent to convent, the peculiar pandemic affected nuns in Germany, France, Italy, and Holland. Religious leaders urged intentional prayer and special masses on behalf of the affected women. When these failed, they turned to exorcisms. Civil authorities opted for decidedly less spiritual remedies, such as flogging, dunking in water, and threats of imprisonment.

As a result of — or in spite of — all of these efforts, order eventually returned, and no further biting or meowing outbreaks have been reported for the past few centuries. Historians have chalked up the unusual episodes to unexplained manifiestations of mass hysteria.

On a positive note, no matter what caused the mass hysteria, it appears that the nuns have kicked the habit. (See what we did there?)