The defining image of World War Z, according to director Marc Forster, is not a zombie biting into someone's flesh but the wildlife montage that plays behind the opening credits, which might best be summed up in the words of one of his characters: ''Mother Nature is a serial killer. The best there is.''
Forster grew up in Switzerland, and as a child spent a lot of time looking at the anthills behind his house.
''I loved watching these insects crawl around,'' he says. Later, he became ''obsessed with swarms of birds and fish, how these swarms communicate with each other''.
The fascination stayed with him when he became a filmmaker. ''I was always thinking I had to implement that image in a film one day, this swarm theory. And once I started working on World War Z, I felt there was no better way to implement that than in a swarm of zombies.''
One of the key set-pieces in the big-budget apocalypse film, produced by and starring Brad Pitt as a UN worker trying to find ''patient zero'', or the first person to be affected in this unexplained plague, involves a swarm of zombies attempting to scale the impossibly high wall that's been erected around Jerusalem.
The symbolism of that wall is rich and conflicted: it protects Jews and Palestinians alike, in a brief and oddly blissful moment of coexistence now the threat has been transferred to an Other more foreign and dangerous than either could ever be. But in Forster's mind, the scene's significance is global, not local.
His zombies trample each other to (un)death in their frantic bid to climb ever higher. ''As the zombie tower is building, it's almost like a feeding frenzy, them going after the last resources with no respect for each other,'' he says. ''They're basically this pack, crawling on top of each other. I thought it's a strong image because that's how humanity is.''
So the zombie apocalypse - the zombocalypse, as the kids would have it - in World War Z represents a planet on the brink of economic and environmental collapse?
''Absolutely, that reflects the time we live in. There are not enough resources for the people that exist.''
It's possible Forster is the first filmmaker to use the zombie horde in quite this way, but he has in no sense betrayed the genre by doing so. One of the key factors in the appeal of the zombie as a fictional device is that it is symbolically malleable.
It is what the linguists call ''overdetermined'', a sign whose meanings (the things it signifies) have overwhelmed the word itself (the signifier). A little like a zombie horde on the move, in fact.
''Zombies are a very elastic storytelling trope,'' the US novelist Jonathan Maberry, whose zombie trilogy (starting with Patient Zero) has been optioned for television, said in 2010.
''They're endlessly fascinating because they play on so many of our fears: the loss of identity in ourselves and our loved ones, paranoia, fear of disease, racism, and so on.''
Above all, he added, they represent ''a constant and universal threat that is implacable and unbearable''.
The seeming endlessness of the onslaught is a crucial aspect of the zombocalypse scenario: the zombie horde represents a threat that is so enormous that it seems impossible to defy.
It can be endlessly substituted for the many things we suspect threaten us but struggle to contemplate: to Forster's resource depletion and overpopulation we might add nuclear war, terrorism, viral epidemics such as HIV, SARS and Ebola, even mindless consumerism.
Each has generated its own iterations of the zombie story, or at least its own readings of the zombie genre. In the hands of left-leaning cultural critics, the film that started it all - George A. Romero's low-budget black and white Night of the Living Dead (1968) - was an allegory for the mindless waste of life that was the Vietnam War.
His 1978 sequel, Dawn of the Dead, with the action moved from a remote farmhouse to a suburban shopping mall, was a devastating critique of the empty lives of American consumers lulled into ignoring the ills of the world by the allure of all that shiny plastic.
The English zom-com Shaun of the Dead (2004) played a variation on the same tune: the repetitive pattern of life in suburban London is barely distinguishable from zombiedom, and in the end almost interchangeable, as Shaun and his best mate - now a zombie, albeit one in restraints - resume the session on the gaming console they'd started before the plague set in.
Writing in the literary magazine Granta in 2011, Naomi Alderman, one of the developers of the app Zombies, Run!, noted: ''The zombie apocalypse is the death of civilisation. It represents the moment when all that becomes important is: do you have food? Do you have guns? We want to practise this in fantasy, to imagine it all the way through, especially in times of economic crisis.''
But she also had a far more personal reading: she couldn't help but hear in the zombie apocalypse a distinct echo of the Holocaust. And anyone who doesn't see in the shuffling, grey-hued living dead of the genre something of the survivor of the Final Solution is surely not looking terribly hard.
Such is the malleability of the genre, though, that it also lends itself to more conservative readings, such as that of the American ''philosophical counsellor'', author and spruiker Mark Dillof. Dillof sees the genre as tapping into an anxiety about ''losing one's autonomy'', a kind of creeping ''paranoia'', albeit one founded in genuine concerns.
All human societies are founded on borders, he argues, the most fundamental of which is that between the living and the dead. ''If the fear of zombies is prevalent today, it is because this is an age in which borders are being transgressed, on many fronts.''
Among them: non-traditional marriage, socialism, communism. ''Such movements as diversity, multiculturalism, globalisation are threatening to dissolve the identity of various nations,'' he adds.
In the zombocalypse scenario, there is in fact precious little of the nation state left to dissolve. Arguably, this points to an anxiety about the rule of law in general and the viability (and reliability) of our political systems.
Nowhere is this played out more explicitly than in the US cable series The Walking Dead. The first two seasons of the phenomenally successful show (its season three finale was watched by 12.4 million people in the US in March) effectively pitted good cop Rick Grimes (Andrew Lincoln) against bad cop Shane Walsh (Jon Bernthal) in a world in which all systems had broken down.
At every turn, they presented their small band of survivors with a choice - between the rule of law and the rule of the gun. In season three, the lines became more blurred as Rick sought to defend his tribe against a rival band of survivors led by an autocratic psychopath known as The Governor (David Morrissey) - and in the process became increasingly like him.
The show has struck such a nerve, season-three showrunner Glen Mazzara told me late last year, because ''people really do believe that some sort of apocalypse is coming and we are going to have to bond together to survive, and the infrastructure of society and government will collapse. They imagine, 'What would my life be like if I had no food, no water and only a couple of guns and had to protect my family and my neighbours'.''
If it taps into the fantasies of the US survivalist movement and its counterparts (of both reactionary and green hues) elsewhere, the show also touches on a fundamental question about what kind of society we would choose if we were to start again.
Would it be compassionate or would it be based on the survival of the fittest? For an America that often feels as if it has lost its way, it's a compelling premise - let's wipe the slate clean, be pilgrims again and see if we can't get this right - even if it's played out against the harshest backdrop imaginable.
Interestingly, race is barely an issue in this post-zombocalypse world. And when that most shameful aspect of America's past pops up, it is dramatically inverted as a samurai sword-wielding African-American Michonne (Danai Gurira) leads a couple of black-skinned zombies, minus arms and lower jaws (so they can't bite or scratch), around by neck chains. The echo of the road gangs of the slavery era (or, indeed, of Australian colonialism) is unmissable.
There's a similar racial flip in World War Z, too. With Pitt's Gerald Lane presumed dead, his wife and children face eviction from the aircraft carrier on which they've been granted refuge.
The man who delivers the news is the deputy-general of the UN, a friend of Lane and a black African. It's a potent ''how would it feel'' moment that makes the whole refugee crisis visceral for even the most disengaged (white) viewer.
For all that, the zombocalypse scenario can satisfy far baser instincts too, as anyone who has ever played a first-person shooter game such as Resident Evil or Left 4 Dead (or the real-world laser-tag version, IRL Shooter) will attest.
In offering up an enemy that is both human and not, and presenting us with a simple kill or be killed scenario, it allows the player to satisfy the killer instinct in a safe environment.
''Zombies are very simple, they don't have a complicated mythology like vampires or aliens,'' says Mazzara. ''They just keep coming at you - they're the never-ending presence of death.''
Writing in the Foreign Policy journal in 2010, Daniel Drezner, a professor of international politics, noted that ''zombie stories end one of two ways - the elimination/subjugation of all zombies, or the eradication of humanity from the face of the Earth''.
That is, in many ways, the choice many of us feel we face in the real world: we keep stumbling through like so many zombies, failing to act upon the threats we face, or we rise up and reclaim our humanity, and our future.
''We're living in times where there are these really big problems,'' said Max Brooks, son of Mel and author of the book on which World War Z is based. ''We've got terrorism, economic problems, unpopular wars, social meltdowns ... we're living in, not apocalyptic times, but I think we're living in fear of the apocalyptic times.''
Stories like his provide people with ''a sort of safe vessel for the end of the world'', he added. ''Zombies are safe. Zombies are manageable. You can't shoot the Gulf oil spill in the head.''
■ World War Z opens today
Sydney Morning Herald