There are no killer clowns. It's an urban legend, influenced by Stephen King's horror novellette "That". It's a typical mass hysteria, too. Compare "alligators in the sewers", "The Blair Witch" and "The Great Depression". Not to mention "ISIS". No such things exist. I know this on the authority of CSICOP, Skeptical Enquirer and James Randi. They never lie and have an excellent track reckord exposing this kind of stuff. Besides, experiments prove that people are bad observers and even worse at remembering details. The killer clowns which some people claim have attacked them are probably just barn owls or the planet Venus, seen under unusual weather conditions.