Colorado Parks and Wildlife: Scary-looking rabbits were hopping around Fort Collins. These weren’t your standard cute, fluffy bunnies; they had horn-like growths protruding from their faces and bodies.

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

DENVER—A group of rabbits in Colorado with grotesque, hornlike growths may seem straight out of a low-budget horror film, but scientists say there’s no reason to be spooked—the furry creatures merely have a relatively common virus.