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Guy Ferrandis, Sony Pictures Classics
John C. Reilly, left, as Michael Longstreet, Jodie Foster as Penelope Longstreet, Christoph Waltz as Alan Cowan and Kate Winslet as Nancy Cowan in "Carnage."

"CARNAGE" — ★★★1/2 — Jodie Foster, Kate Winslet, Christoph Waltz, John C. Reilly; R (language); Broadway

They try to keep things civil. It's what enlightened urban bourgeoisie do. Yeah, one family's son whacked the other family's son in the face with a stick in the heat of an argument at a New York City park. But they're 11. And we've seen the altercation under the opening credits. No sense losing one's cool over that.

But "Carnage" is all about losing one's cool. Two couples — four parents — meet and over 75 increasingly testy and often hilarious minutes, they charm, bicker, cajole, parse words, reason with and bait one another in this very entertaining Roman Polanski film based on a French play. Alliances shift at characters attempt to defuse the debate.

It's one couple vs. the other couple, then one husband and the other wife against the other two, then wives team up against husbands. Yasmina Reza constructed a delicious "Who's Afraid of Virginia Woolf?" for the age of helicopter parents — hovering over their kids, obsessing over everything.

One minute, it's the guys (John C. Reilly and Christoph Waltz) shrugging, "Boys will be boys," the next it's the victim's mom (Jodie Foster) shrieking "Their son is a threat to Homeland Security!"

Then the guys mix it up, the housewares seller (Reilly) pushing the buttons of the corporate lawyer (Waltz). The kids issue fades into the background as egos and value systems clash.

"I held my own, right?"

Was the one boy "armed" or just "carrying a stick?" The wording matters to the lawyer and his businesswoman wife (Kate Winslet). That's because the other parents are insisting on their boy's victimhood.

Michael (Reilly) tries to agree with everybody at once. His wife, Penelope (Foster), is a shrill idealist who wants to hold the whole world accountable. Alan (Waltz) has this crisis at the office and a cellphone that won't stop ringing. And Nancy (Winslet) would love to find common ground, get this meeting over with and have the boys shake hands.

"So many parents just take their child's side," she says, affecting a conciliatory and superior air. Then Penelope says something to bring things back to a boil: "I don't understand how you can be so uninvolved!"

Foster is the most wound-up of the players, but there isn't a bad turn in this quartet. Waltz's imperious, crude, cruel lawyer stands out. He's riveting as a guy who thinks of himself as some sort of macho Wall Street killer, a fellow with a gift for speaking truths that none of the other three want to hear.

"Carnage" is very close to a filmed play. But Polanski, filming this mostly in close-ups and tight, tense two-shots, plops these four into a crucible and grinds away. And once the coffee's been sipped and the whiskey has been uncorked, ugly truths about prejudices and pets and parenting, couples with secrets, men married to their work and women married to their causes, pour out.

There's no literal blood, no entrails or visible battle wounds. But they titled this one right. When these parents meet, argue and part, what's we're left to ponder is a field littered with the dead and wounded — carnage at its most personal and emotional.

"Carnage" is rated R for language; running time: 80 minutes.