Filmmaker M. Night Shyamalan is known for creating twist endings. What he should be known for is twisting conventional genres. Sometimes it works, as it did in The Sixth Sense, Signs, and Unbreakable. And sometimes it just falls flat.
In The Happening, Shyamalan plays off a couple of different genres, but most obviously he works with “nature gone wild” — a subgenre of science fiction and horror with a resumé dating back at least to 1954’s Them! In its science fiction manifestation, “nature gone wild” usually involves genetically altered species of animals or insects: giant irradiated ants (Them!), giant chemically mutated bunnies (Night of the Lepus), giant irradiated brain-eating talking crabs (Attack of the Crab Monsters). You get the picture.
In its horror manifestation, “nature gone wild” sometimes involves natural breeding gone dangerously out of control (The Swarm), but most often it involves some kind of malign natural sentience. That is, some element of nature, without any mad science assistance, has developed an apparently conscious will to kill humans. The two most famous examples involve: 1) a lone shark preying in shallow waters, and 2) the interspecies flocking of homicidal birds (c’mon, you know the titles!).
In The Happening, Shyamalan blends “nature gone wild” with what I jokingly refer to as the “siege on a farmhouse in Western Pennsylvania” subgenre of horror — i.e. the George Romero Dead movies and their descendants, including the British Dog Soldiers and Shyamalan’s own Signs. (Curiously, the original “siege on a farmhouse” movie took place in Bodega Bay, California and involved the interspecies flocking of homicidal birds).
In addition to alien invasion movies and Swedish existential ones, Shyamalan's Signs took on Night of the Living Dead (arguably the most famous film by a Pennsylvania filmmaker) and did a credible job of it, turning flesh-eating zombies into aliens cultivating humans as food and directly assaulting the protagonists’ farmhouse overnight. The Happening pays homage more to Dawn of the Dead, as the protagonists flee the city into rural Pennsylvania, hoping to find a safe haven from the assault, only to find a string of abandoned, hostile or semi-abandoned farmhouses... and no abandoned shopping mall!