 In 1996 sceptic Joe Nickell objected that correlation is not causation, raised several objections to Levengood's methods and assumptions, and said "Until his work is independently replicated by qualified scientists doing 'double-blind' studies and otherwise following stringent scientific protocols, there seems no need to take seriously the many dubious claims that Levengood makes, including his similar ones involving plants at alleged 'cattle mutilation' sites.