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

As weird and concerning as they appear, the virus that causes the dark, wart-like horns or tentacles to grow on cottontail rabbits is relatively common and usually not anything to worry about.

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