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, CPW

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

Some cottontail rabbits in Fort Collins, Colorado, have been drawing attention because they have wart-like growths on their faces that look like horns.