i think it is obviouse that its the plants and mnight does this on purpose. however, i think since he changed the title to the happening, it directs us to the possibility that although in this instance its the plants, the happening could be anything cataclysmic that forces us to question society, life, ourselves, etc.

the mis en scene (aka bad acting, one dimensional characters, weird dialog) is in a 1950s horror movie style. back then these movies symbolized the threat of nuclear war with the ultimate threat; Russia. In the happening, the ultimate threat is ourselves. thats why the disease causes humans to "kill themselves"

i think the strange relationship between the main charactors is also in reference to the attitudes of women and marriage in the 1950's. people then were ignorant to the power of women and often society tried to keep them in their place. i think this is symbolic of how we treat mother nature, ignoring her true power and using technology to subdue her.

pretty out there i know. its just my thoughts. i loved this film and wanted to discuss it with some other shyamalan fans. thanks for reading my rant.