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

Rabbits spotted in Fort Collins, Colorado, with hornlike growths are infected with the mostly harmless Shope papillomavirus, a virus that inspired the jackalope myth and contributed to early cancer research.

Colorado Parks and Wildlife say rabbits in Fort Collins are infected with rabbit papilloma virus, causing horn- or tentacle-like growths.