Though the horned rabbits aren’t a danger to humans or pets, Van Hoose advises people to keep their distance from the creatures, as they should with any wild animal, because rabbits can pass along other pathogens. “Once you realize these probably aren’t harmful to rabbits, you can kind of appreciate the science at work,” she says.

Photos of the cottontails inspired nicknames like “Frankenstein bunnies,” “demon rabbits” and “zombie rabbits.”

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.