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

Wild rabbits in Fort Collins with tentacle-like growths are infected by a virus called Shope papilloma virus, often mistaken for the mythical jackalope.

Recently, some wild rabbits have been seen in the U.S. with "horn-like" growths spurting from their heads that are caused by a viral infection, according to experts.