Dogs are funny. They're funny ha ha and funny peculiar. Who can resist grinning while watching a Shar-Pei stroll down a city street, sticking out its tongue when passing the office of a plastic surgeon? Who can keep a straight face while taking in the sight of a terrier digging and digging for nothing in particular, or the look on the face of a bull terrier who bears a striking resemblance to its human daddy, or the arrogant perambulations of an Afghan Hound?

Funny as canines are, though, people are more bizarre in every way. People, too, are funny ha ha and funny peculiar, and Christopher Guest's movie "Best in Show" is ultimately not about the parades of pooches that pass across the picture screen but about the people who are proudly possessed by the four-legged beasts. The humans are the ones who go for the cups, for the blue ribbons. Each wants to be the champion, the best-in-show, and like many a neurotic parent, the handlers and owners live vicariously through their four-legged friends.

"Best in Show" centers on the Mayflower Dog show, held in Philadelphia and modeled after the world-famous Westminster Dog Show held in February of each year in New York's Madison Square Garden. Filmed entirely in Vancouver with a realistic mock dog-show setup, "Best in Show" proves that Christopher Guest can get absolutely hilarious performances from his actors by holding them on the loosest of leashes and allowing them to improvise their way through this top-notch comedy. There's no secret to Guest's expertise at directing: just choose some of the same performers you embraced for your previous mockumentary, the 1997 feature "Waiting for Guffman (about the mounting of a musical show celebrating the 150th anniversary of Blaine, Missouri), tell them how to get from point A to point B, and let them decide how to get there--as though you were giving a brace of bloodhounds a sniff of a bad guy's clothing and allowing the lovable creatures to track the felon down.

While those familiar with dog shows know that the handlers and owners are for the most part stable people (they come inevitably from the suburbs), Guest obviously has no need to show these solid, all-American types, instead taking endearing aim at the eccentric minority who give the competition its Purina gourmet flavor. Yuppie lawyers Meg (Parker Posey) and her husband Hamilton Swan (Michael Hitchcock) would be most recognizable to big city dwellers in the movie audience while conservative menswear salesman Gerry Fleck (Eugene Levy) and his bubbly wife Cookie (Catherine O'Hara) represent your typical suburbanites. Other idiosyncratic show people include a happy gay couple, the flamboyant handler Scott Donlan (John Michael Higgins) and his partner, hair salon owner Stefan Vanderhoof (Michael McKean); and Sherri Ann Cabot (Jennifer Coolidge) as the zoftig young wife of a senile industrialist (Patrick Cranshaw), who has hired fellow lesbian Christy Cummings (Jane Lynch) to show their Standard Poodle. Others in the side-splitting ensemble are the straight-laced Kennel Club president Dr. Theodore W. Millbank III (Bob Balaban), Graham Chissolm (Don Lake) as the show's chairman, Trevor Beckwith (Jim Piddock) as the classy co-announcer of the event, and Buck Laughlin (Fred Willard), whose manic role as the show's announcer proves the comedic highlight of the film.

Anyone in the movie audience who listens to stand-up comic Fred Willard discuss the events would learn virtually nothing at all about dog shows but a lot about how many pounds he can press as a middle-aged man (315) compared to what he could do in his more potent days (500) plus some side commentary about his visits to a proctologist. Obviously more attuned to what goes on in sporting events involving only two-legged jocks, he metaphorically describes the panorama at the Mayflower in terms of baseball and football, reminding us that when the final competition takes place-- seven dogs lined up with only one to get the cup--we're in "the bottom of the ninth with the final batter at the plate."

While Willard--and not the winning dog--steals the show, Eugene Levy and Catherine O'Hara turn out the most riotous performances of the dog owners. They, more than any other couple, play their roles absolutely straight with the bespectacled Levy (superb as the stiff-laced father in "American Pie" who wants to explain the birds and the bees to his hormone-crazed son) being driven nuts by the fellows he meets who all seem to have dated his vivacious wife. To add to his misery, his character, Gerry Fleck, cannot dance because he has two left feet. Literally. Parker Posey impersonates her usual high-strung character, the sort of urban neurotic that Jane Fonda played in "California Suite," bickering constantly with her similarly disturbed husband who tries to check into the hotel with no balance on his credit card, having lost the dog's favorite toy to boot. Their psychoanalyst back home is the only person who could in any way be regarded as their friend: he is paid to listen to how their sex lives are ruined because their similarly neurotic Weimaraner, Beatrice, glowers at them while they engage in positions recommended by the Kama Sutra.

The only suspense in the story rests with the question: who will take top honors at the Mayflower show? My own pick differed from that of the judge, but who needs suspense when you're rocking with laughter at the film with the most inventive improvisational dialogue of the year?