The cottontails recently are infected with the mostly harmless Shope papillomavirus, which causes wart-like growths that protrude from their faces like metastasizing horns.

Viral photos have inspired a fluffle of unflattering nicknames, including "Frankenstein bunnies," "demon rabbits" and "zombie rabbits."

Rabbits with black, hornlike spikes growing on their heads and other odd or unslightly protuberances are not dangerous and won't infect humans or other species, Colorado Parks and Wildlife said Wednesday, following days of social media posts about sightings of "Frankenstein bunnies," "demon rabbits" and "zombie rabbits" in and around Fort Collins.