Some of these groupes d’auto-defense have themselves run afoul of police. When five teens in Mulhouse attempted to organize an anti-clown resistance group⎯armed with a tear-gas canister, a baseball bat, a telescopic baton, and brass knuckles ⎯they were promptly arrested.

The Police Nationale issued an official warning to both clown and anti-clown factions on October 24, warning that “anyone, regardless of whether they are an aggressive clown or a clown-hunter, found with a weapon in public thoroughfares will be arrested."

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What exactly is behind France's clown outbreak? The French police have blamed social media, as well as foreign influence. After a group of chainsaw-wielding clowns appeared in front of a primary school in northern France, the police suggested on Twitter that the clown gangs were taking their cues from the 1974 U.S. film The Texas Chainsaw Massacre.

Some of France’s major newspapers, too, have cited trends in Italy and America as possible sources of evil-clown inspiration. Le Monde speculated about the influence of DM Pranks, a YouTube account run by the Italian duo Diego Dolciami and Matteo Moroni, whose trilogy of "Killer Clown Scare Prank" videos has earned tens of millions of views. The videos show Dolciami in a clown costume smashing dummy corpses with a mallet while Moroni films the reactions of terrified passersby. Le Monde also flagged the recent emergence of a scary clown in Wasco, California, as well as the start of a new season of the TV show American Horror Story, which features the coulrophobia-inducing Twisty the Clown. And as my colleague Sophie Gilbert noted recently, U.S. and Italian media each have a long-standing role historical role in scary-clown culture, from as early as the 1892 Italian opera Pagliacci, which features a murderous clown exacting revenge on his unfaithful wife.

But France's history with killers in face paint predates even Pagliacci. In 1836, the famous mime Jean-Gaspard Deburau struck with his cane a street urchin who insulted him, killing the boy instantly. That violent outburst led to a 19th-century celebrity trial, in which Deburau was ultimately acquitted. The case generated intense curiosity about hearing a mime speak.

The modern French outbreak of evil clowns, meanwhile, has stoked interest in the perpetrators' possible motives. But, like Deburau, who disappointed French audiences when he finally did speak only to defend himself, France's evil clowns may turn out to have unremarkable motivations. One clown-costumed teenager who terrorized the town of Périgueux with a plastic knife just says he just did it as a joke (pour faire une blague).