Guardian: In The Happening, nature strikes back at mankind by releasing a toxin from trees that causes people to commit suicide. Plants release a great number of volatile compounds. If you walk through a pine forest, or sniff herbs, you’re smelling them. And we’ve known for a long time that there are mind-altering substances in plants such as cannabis and the peyote cactus, but these are not airborne - or at least not until you smoke the cannabis.The Happening suggests, correctly, that vegetation can …