Nearly everybody who watched this had misunderstood it's genius.

Rating: 9/10 (21 November 2015)

I swear this movie is a satire on Stephen king, purely in the aspects of acting and direction. If you've watched enough Stephen King, you'll know what I mean.
As for the story and plot, a more serious note is taken.
See, to most people, The Happening made no sense. "Oh plants killing people, right, sure"
But it actually makes perfect sense.
If you don't get what I'm saying, I urge you to watch it again with this in mind: Plants are living organisms. Organisms have two instincts; survival and reproduction.
In order for these first two instincts to succeed, it requires a third instinct: defense.
Still confused?
Let me answer a few common questions. "Why so sudden?" Well it's not sudden. A plant has few forms of defense, and one is to release toxins. Collective flora is damaged and seeks out the cause. It releases toxins to battle the cause, and every time a toxin doesn't work, it's mutates the toxin hoping to find the right compound before it's too late. The toxin helped against pollution, but not enough. The toxin didn't work on material man made objects like the concrete of the power plant (the vision of which was a glaringly obvious clue) so the flora tries again, until it has found one that causes allergies. This isn't enough, and further toxins cannot defeat the human immune system. Eventually after 100,009years of humanity, flora formulates a toxin that works, and releases this toxin in areas where human activity is high enough for the plant to recognise the energy (hence the man talking calmly to his plants).
You do the rest