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.

Rabbits in northern Colorado have been spotted with bizarre, somewhat grisly horns on their face. Shope papillomavirus is known to affect only rabbits and hares, not humans or other animals, says Kara Van Hoose,