People in Fort Collins, Colorado, are seeing rabbits with black horns and tentacles that wouldn’t look out of place in a horror movie. Though frightening, their appearance is caused by a known virus that’s harmless to humans.

Journalist Amanda Gilbert documented the town sightings in an article for local outlet 9NEWS last Friday. Colorado Parks and Wildlife officials say the rabbits are afflicted with a virus that causes wart-like projections to emerge from their faces—a condition that likely even inspired folk tales in the past about horned rabbit cryptids.

“It looks like it was black quills or black toothpicks sticking out all around his or her mouth,” Fort Collins resident Susan Mansfield told 9NEWS. “I thought he would die off during the winter, but he didn’t. He came back a second year, and it grew.”

The rabbit germ is called the Shope papilloma virus. It’s a cousin of the human papillomavirus, and like some HPV strains, SPV can trigger the formation of growths, typically made out of keratin. The virus is primarily transmitted through biting arthropod vectors, such as mosquitos and ticks, though it may also spread through close, direct contact with infected bodily fluids (the growths themselves don’t carry the virus).

Papillomaviruses are usually tuned very specifically to their hosts, SPV included, so they aren’t a threat to people. Rabbits can live with the infection and even lose the growths over time, but SPV can also turn dangerous. The growths can become large enough to interfere with eating, and they will sometimes transform into malignant tumors that spread elsewhere in the body. Infections are rarely seen in domestic rabbits, however, and most commonly affect cottontail rabbits in the wild.

The growths can look like deer antlers, and many scientists argue this uncanny resemblance helped foster the North American myth of the jackalope and similar horned rabbit creatures. As with many things, though, capitalism is also partly to blame for the cryptid’s enduring popularity. In 1977, brothers Ralph and Doug Herrick claimed that they were the first to market taxidermized jackrabbits fitted with deer antlers as jackalopes in 1934. And even today, many gift shops and tourist attractions still sell these fauxalopes.

SPV isn’t just the inspiration behind the jackalope. Its discovery in the 1930s helped confirm that certain viruses can trigger cancer, and scientists have long used it as a model in the lab to better understand HPV-related cancers.

The real-life jackalope may be harmless to people, but Colorado Parks and Wildlife officials say people still should steer clear of wild rabbits infected with SPV. Indeed, we can never be too cautious.