This video shows Cleve Backster, a polygraph tester at the CIA, explaining how his experiment on plants changed his life forever. On a particularly boring February 2, 1966, Backster noticed a houseplant in his office and decided to perform a polygraph test on it while giving it some water.

A polygraph test measures pulse, respiration rate and perspiration. Backster wanted to induce anxiety in the plant, so he decided to set one of its leaves on fire. But before he could even do it, the polygraph registered an intense reaction on the houseplant. Backster was bewildered: not only had the plant demonstrated fear, it had also read his mind. Backster concluded that plants had some undiscovered sense (he called it “primary perception”) that could detect and respond to human thoughts and emotions. Scientists were less convinced. No one had the same results as Backster.