The most obvious similarity between The Happening and Romero's zombie movies lies in what happens to the infected. They don’t become flesh-eating zombies, of course, but they do become something equally alien and horrifying to the non-infected: suicidal automatons, often wreaking (or seeking) havoc on their own bodies. The Dead films are not just about zombie noshing. They’re also about loss of will and becoming one’s own worst nightmare.

Shyamalan intentionally, even strategically, inserts The Happening into the lineage of some of Alfred Hitchcock's and George Romero's greatest work. So how does it match up?

In The Birds (Hitchcock's first motion picture after Psycho), the master is at the top of his form. The Birds is sort of an apotheosis of the “nature gone wild” film. In it, birds mass and mount inexplicable (and unexplained) assaults on humans, attacking children as well as adults.

The Birds takes its time in revealing the threat. Starting out as a sort of screwball comedy about the wacky interactions between a wealthy socialite and a young lawyer, the first bird attack – a single swoop down on the socialite – comes at least 20 minutes into the film. The attacks build and build, though, until swarms of birds are racing down the farmhouse chimney, pecking their way through ceilings and doors, and massing for what seems like miles around the farmhouse. In the end, we don’t know the cause of the event. We don’t even know if it’s isolated to Bodega Bay and environs or if it’s the first wave of a worldwide apocalypse.

Night of the Living Dead similarly paces itself. An isolated attack in a graveyard leads to the discovery of an abandoned farmhouse, which leads to the grisly discovery of a mutilated corpse, which escalates towards a full-scale assault. We get the news in waves. The living, first in ones and then groups, descend on the farmhouse. Then come the dead. The film is well underway before we hear the first newscast explanations for this epidemic of homicide.

But the slow, deliberate tease is not necessarily crucial to the genre. Drawing on the mythology of its antecedent, Dawn of the Dead places us already in the middle of the crisis, opening with a SWAT team trying to take down zombies while talking heads try to explain the phenomenon.

The Happening tries it both ways — starting off fast, but teasing it out slow. Like Dawn of the Dead, The Happening opens with a large-scale crisis. Mass suicides occur in Central Park and nearby. But by the time Philadelphia hears, the only questions are how large the crisis is and what's causing it. Our awareness of the size of the catastrophe, like the characters', develops slowly, while our sense of the cause evolves over the course of the film.