"Whatever it is,* it's not happening** ninety miles from here".***
*It's plants. Plants, because they're not our friends, are emitting a neurotoxin that causes people to babble mindlessly, freeze, then commit mass suicide. The plant angle is obvious within the first thirty minutes, but the movie treats it like a tasty but fattening tub of ice cream, to be doled one stingy spoonful at a time, until your face is covered in Haagen Dasz and your stomach aches, and then you're supposed to go, "Hey! This is ice cream! Thanks for the sweet suspense, M. Night!"
Of course, it's not just enough to have people die. The victims have to off themselves in the most grotesque and cinematic style possible. Plants don't just want to stage our extinction. They have production values. Are plants auditioning for Hollywood? They can't do any worse at filmmaking than us humans.
On the other hand, this could be nature's revenge on us for flash mobs.
**For reasons that likely have to do with M. Night Shyamalan's attempt to inject meaning into a B-movie, the vaporously vague term "happening" is used again and again with all the intensity of a dripping tap: "What's happening?" "There appears to be an event happening" "Can this really be happening?" "The event must have stopped happening already". This pretty much kills whatever tension that Shyamalan is trying to generate with his comically stunned and inadequate characters. Imagine Titanic if people just stood around on deck and said "There appears to be a submersion taking place somewhere" or "By the time the submersion reaches this area, drowning will have occurred to persons who are us, or other persons currently occupying this area, either at present or in the near future".
The first 'happening' occurs in New York City, then in increasingly smaller centres around the Northeast United States. As the puny humans flee, they find that no place is safe. A group of stranded travelers crowd into a diner and watch a television reveal
***I'm not sure if that's the line verbatim. I found a copy of the script online and checked it out, but it was an early (and much, much better) draft, and the diner scene has changed. So I can't be certain that what I'm giving you here is completely accurate. But there is no fucking way I am sitting through that crippled zombie of a film again.