Comedians often say the best humor comes from real-life — or at least, true-to-life — situations, which is probably why filmmaker-of-all-trades Christopher Guest's big-screen comedies work so well. Their sometimes painful truthfulness also explains why they have found such an appreciative audience.

His mock-documentary "Waiting for Guffman" was a delight for anyone who's ever been involved in either professional or amateur theater. (Though it was a minor box-office hit at best, it's gone on to become a genuine cult favorite on video.)

And Guest's latest, "Best in Show," takes an equally skewed but slightly less funny look at pet owners. And though the pseudo-documentary style dictates that it must have a certain story structure, it still provides fertile ground for improvisation, a circumstance under which his ultratalented cast thrives.

Looking at the film in retrospect, it's probably an idea that could have been done earlier — a fictional, behind-the-scenes look at one the most prestigious pet competitions in the world, the annual Mayflower Dog Show.

It's a contest that pulls animals and trainers in from all over the country, including Harlan Pepper (Guest), a North Carolina fishing-shop owner who's hoping his Bloodhound, Hubert, will win the blue ribbon for Best in Show.

But he's got stiff competition from Gerry Fleck (Eugene Levy) and his vivacious wife Cookie (Catherine O'Hara), who are bringing their Norwich Terrier, Winky, to the contest.

Similarly confident in their chances are hairdresser Stefan Vanderhoof (Michael McKean) and his partner, Scott (John Michael Higgins), the proud owners of a Shih Tzu, Miss Agnes, as well as the Swans (Michael Hitchcock and Parker Posey), bickering yuppies whose Weimaraner, Beatrice, has become as neurotic as they are.

However, the real frontrunner is two-time champ Rhapsody in White (a Standard Poodle), whose wealthy owner (Jennifer Coolidge) has hired an ace trainer (Jane Lynch) to assure another win.

Comedywise, the film gets off to a slower start than "Guffman," and some of the humor here seems either a bit forced or downright mean-spirited in places (the gay community may be a tad miffed by some of the characterizations here).

But things turn around considerably upon the first appearance of Buck Laughlin (a never-better Fred Willard), whose clueless commentary on the competition is the film's brightest spot. (Though the exasperated reactions from Jim Piddock, a Brit playing Laughlin's broadcast partner, are a close second.)

Not that the rest of the performances are bad, mind you. In fact, Levy is spot-on as O'Hara's jealous husband, while McKean, Higgins and Guest all get their moments to shine (particularly the intentionally awful ventriloquy performed by the latter).

Even Hitchcock and Posey, whose on-screen arguing gets pretty shrill, are well-served by a fitting ending to their story line.

"Best in Show" is rated PG-13 for crude humor, most of it sexual in nature, as well as some scattered profanity. Running time: 89 minutes.

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