Okja may not be the year’s best film, but it could well contain the year’s most riotously entertaining 15 minutes: a helter-skelter chase which climaxes with a minivan-sized mutant pig galumphing though a shopping mall. If you can imagine a Judge Dredd comic strip adapted for the big screen by Buster Keaton, you’ll have some sense of how bizarre, inventive and gleeful this frantic set-piece is. And if the rest of Bong Joon-ho’s satirical sci-fi romp can’t quite reach the same stratospheric levels of fun, well, what can?

The mutant pig in question is the property of a New York-based agrochemical corporation with a dubious past. In a fast and flashy prologue, the corporation’s boss, Lucy Mirando (a white-wigged Tilda Swinton) tells a crowd of journalists that a “miracle” animal has been found on a Chilean farm. Looking more like a floppy-eared hippo than a common-or-garden porker, this wonder-beast is the ultimate meat provider: low-consumption, low-waste, gigantic and delicious. Twenty-six of its offspring are to be packed off to farms around the globe to see which environment suit the breed best - and one of the mega-piglets, named Okja, ends up being raised on a lushly forested Korean mountainside by a good-hearted girl, Mija (Seo Hyun An), and her grandad (Byun Heebong). 

Thanks to some cutting-edge CGI, and a flawless performance by Seo Hyun, it’s easy to believe that the elephantine Okja is a flesh-and-blood creature which has been trotting contentedly around the woods for years with its beloved Mija. But after a decade, the time comes for Okja to be shipped back to Mirando’s corporate headquarters in New York, and the film switches from The Jungle Book to King Kong. Mija is furious that her gentle and highly intelligent best friend has been stolen from her. Determined to steal it back, she dashes from the farm to Seoul, where she is helped and hindered by an Animal Liberation Front task force led by the dapper and deceptively calm Jay (Paul Dano).

Okja may be a film about a humungous pig, but Jake Gyllenhaal is the biggest ham in it by far

The idyllic forest scenes are so charming, and the subsequent urban slapstick scenes so hilarious, that it seems a shame that Bong and his British co-writer, Jon Ronson, didn’t cut some of the swearing and the vicious violence. If they had, their frequently witty and twistily plotted film would have been a family adventure to beat The BFG and Pete’s Dragon. That is, it would have been a 21st-Century ET The Extra Terrestrial, except with a bilingual script and a hard-hitting pro-vegetarian message. Like that classic, Okja manages to balance its cartoonish concept and its wild action with characters we can can care about. Even Swinton’s Cruella De Ville-ish villain is humanised: beneath the power suit of a preening CEO, she is a damaged little girl who still practises her signature in her notebook and has braces on her teeth.

But Jong loses control of the film’s tone in its second half. Once the story moves from Seoul to New York, there is a gradual increase in implausibility until, eventually, the anything-goes wackiness overshadows the sombre indictment of industrial meat production. This misjudged zaniness is embodied by Jake Gyllenhaal. Playing a thickly-moustached, squeaky-voiced celebrity vet, he doesn’t seem to know what he’s doing, but for some reason it involves flapping around like a marionette being operated by an inept puppeteer. Okja may be a film about a humungous pig, but Gyllenhaal is the biggest ham in it by far.

Don’t let that put you off, though. A slightly shorter, slightly more disciplined Okja might have been better, but the one Bong has made is still a joy. And it does pose a tricky question to anyone planning to grab a burger after seeing it: if the thought of a CGI animal being turned into sausages is so upsetting, why are we willing to eat real ones?

★★★★☆ 

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