HOW DO YOU SEDUCE AN AMERICAN audience, one that's lost the taste for subtitles and the pleasures of complex moral tales, into watching a foreign-language film with no stars, no familiar names, no recognizable way in? Well, you could start with the promise of flesh, of naked boys without an ounce of fat, or a crease on their faces, of the girls beneath them and the voluptuous woman whose breasts the boys sink into like grateful children. You could theorize about what gives the film's sex its sizzle, describe all the freeform humping and flailing, with the boys and girls equals under the sheets, if not always above. Along the way, you could also mention the exotic, faraway places — first Mexico City, then deeper into a land where, with each passing mile, the faces appear more Mayan, inscrutable, as the blue of the sky slips into the blue of the water. Whatever you do, though, don't mention that what gives all this flesh and scenery their shiver isn't just beauty or exoticism, but the dirtiest word in movies — politics. It's no wonder director Alfonso Cuarón keeps his characters half-dressed for much of the film: With so little on their bodies, it might be possible to forget how much he has on his mind.

Or would be if his film weren't so smart from the get-go. Y Tu Mamá También is the fourth feature by the Mexican filmmaker, and easily one of the sexiest and funniest films about class struggle ever made. Written by his brother Carlos, who also wrote the director's first feature, Love in the Time of Hysteria, the film is smarter than its raunchy good humor, its fart jokes and circle jerks, initially suggests. Early in the trip, its three main characters, two Mexican boys and a young Spanish woman, enter a restaurant with peeling paint and a clutter of hard metal chairs, and begin swapping love stories. As the troika sits laughing, the camera follows an older woman, draped in a black shawl and an air of piety, who takes us into a backroom where other women listen to a radio, talking and preparing the food that the travelers soon will be eating. The scene is so unexpected and immediately entrancing — one withered matron executes a jig while a boar's head stares up from the chaos of a prep table — that you regret it when the scene ends. The director may be seducing us with intimate intrigue, teasing us with the promise of hot monkey love and wild (that is, foreign) booty, but in his film's voice-over narration, and with his camera, he's telling us other stories, those usually heard only behind closed kitchen doors.

It's sly storytelling this, a narrative fan dance in which you keep looking for the next bit of nasty only to come up with art and a flash of social realism. The three travelers — two hormonally combustible teenagers floppy as puppies, Tenoch and his best friend, Julio (Diego Luna and Gael García Bernal), and an unhappily married Spanish woman with pooling eyes named Luisa (Maribel Verdú) — have met at a wedding where they've discovered that Tenoch and Luisa are cousins by marriage. All three shimmer with beauty and youth. They have the glow of hope, of a radiant future (even for sad Luisa), and now they're on their way south to a beach that doesn't exist, called Heaven's Mouth. It's clear from the way that they keep sliding one another looks that in between the boys' invitation to Luisa and her acceptance, something of consequence has happened, and that something else, too, looms on the horizon. From the way Cuarón keeps adjusting the heat inside the battered station wagon even as he guides our attention — first gently, then with increasing insistence — to the sun-blasted world outside, it soon becomes just as apparent that this is no minor diversion, no lazy roundabout, but a voluptuary's journey into the unquiet heart and mind of his native country. Here, all roads lead straight to Mexico.

IN THE AMERICAN ROAD MOVIE IT'S the travelers that count, not those left behind. In Y Tu Mamá También there are times when it feels like the whole of Mexico has thumbed a ride. There's Tenoch's doting Indian nursemaid and his corrupt politician father, who once fled to Canada after selling contaminated food to the poor. There's Julio's left-wing activist sister, and Luisa's literary fraud of a husband, who went to Europe for art and came back with a wife. There are passersby, fellow travelers, cows, chickens and even ghosts haunting the road. If the boys and the woman don't always notice the world beyond the dashboard — a wedding party crammed into an old Volkswagen Bug, soldiers with machine guns hassling peasants as they hawk their wares — the camera and the narrator do, though with no finger-wagging. As the road unwinds and the travelers share their histories and secrets, the land itself, at first only glimpsed in blurred bits and pieces, begins to transform into a palpable presence, almost another character, mysterious, tragic, as weighted with wonder as it is littered with reality. Not that any of this is noticed by the trio so busily giggling, bragging, self-mythologizing, self-imploding, smoking dope and listening to Brian Eno, who drones “failing to remember why we came, came, came” right before the boom box cuts out. (For the rest of the trip, it's nothing but mariachi radio.) One day and night out of Mexico City, and already Julio and Tenoch are tourists in their own country.

You have to wonder if the director knows how it feels. Cuarón is best loved in this country for his 1995 film A Little Princess, a lovely, unsentimental retelling of the Frances Hodgson Burnett novel about a boarding-school student who goes from privilege to poverty. But he's best known for the movie he made three years later, the high-profile flop Great Expectations, an inert venture less notable for its fealty to the Dickens novel than for its polychromatic greens, a whirling color wheel of absinthe, emerald and opalescent bile. Neither the movie nor its stars are as bad as many reviewers insisted, but while Ethan Hawke and Gwyneth Paltrow did their best, they also came off as afterthoughts to the overwrought production design. The film was a bummer, especially for what it seemed to portend for its director. Then, instead of failing further upward, as do many Hollywood inductees, securing even bigger budgets with yet more stars, Cuarón threw himself a lifeline. He landed a script worthy of his talent and, whether out of pain or wisdom, learned not to indulge his and cinematographer Emmanuel Lubezki's visual gifts: There isn't a shot in the new film that feels like showboating, or a setup that's superfluous. Having become overly fond of art-directing the world into claustrophobic perfection, Cuarón discovered how to pull art from the messiness of life. He found the balance between the world as it is and the world as he'd like it to be, which may be why, for the first time, his characters live and breathe with such sympathetic force.

HE ALSO WENT BACK HOME. IT IS telling that both Love in the Time of Hysteria and Y Tu Mamá También, the only of Cuarón's four features to be made in Mexico, open with a man and woman screwing in bed. These scenes share a similar, unspecified point of view (the camera hovers over the couples for a nice, long, blushingly intimate look) and an infectious vibe of rollicking pleasure. There's nothing prurient about either bedroom romp, though for American viewers the juicy eroticism in each film, and the ease with which the actors throw themselves into such intimacy, only underscores the desiccated puritanism of our own movies. Love in the Time of Hysteria is a shrill, unfunny sex farce about a Lothario who mistakenly believes he's HIV-positive, but it has a looseness of form and an irreverence — toward politics, toward sex, toward social orthodoxy — that had gone completely missing by the director's second Hollywood production. With Y Tu Mamá También, Cuarón has returned to Mexico, to its bodies and their stories. At one point in the film, Luisa describes meeting a 98-year-old woman who remembers everything in her life since she was 5, an entire century held in her body. There are all sorts of bodies in this film — some ripe and unbent, others stooped with age and work, each with a story Cuarón tells with passion, tenderness and not a jot of compromise. “Imagine,” says Luisa, “everything she's lived.” Imagine remembering all that you've lived; worse yet, imagine forgetting.

Y TU MAMÁ TAMBIÉN | Directed by ALFONSO CUARÓN | Written by CARLOS CUARÓN Produced by SERGIO AGÜERO | Released by IFC Films | At selected theaters | Opens March 15

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