Maybe Tim Blake Nelson just got tired of being so serious. The actor and writer -- whose previous films as a director have questioned the existence of God (Eye of God), retold Othello in a high school setting (O) and examined the conscience of Jews who worked with their oppressors in Nazi concentration camps (The Grey Zone) -- goes absolutely bonkers in Leaves of Grass.

The film is so outrageous with its ethnic caricatures, hokey plot and twin-brother mix-ups that you know the whole thing is a lark. And that's well before a crazed orthodontist shows up, waving a gun.

Nelson certainly deserves to do a comedy. The trouble is he really doesn't know how. This is a flat, unconvincing film with its tone far off base. Leaves will get laughs, all right, but not the right kind. This head-shaker belongs strictly in festivals (it premiered at the Toronto fest). As usual, though, Nelson attracts enough high-profile actors that the film will find its way into commercial theaters -- which will be a mistake.

The first goofy notion is the film's very premise. Edward Norton plays identical twin brothers who behave as if they were separated at birth and given to mad scientists at opposite ends of the earth.

Brother Bill is an academic cover boy, a classical philosophy professor at Brown. He is an articulate, immaculately dressed man who prides himself on his self-control and Ivy League accent. Brother Brady is a backwoods Okie pot farmer. Outfitted in tattoos and a shaggy beard, he's unable to speak his rural English without obscenities and grammatical horrors in nearly every sentence.

(The latter is not true when he extols his pot-growing capabilities. Then he sounds like he has a Ph.D. in botany and chemistry, one of the film's many inconsistencies.)

The brothers haven't seen each other in years. For that matter, Bill doesn't care if he ever again sees his mother, who's in a rest home. She is played by Susan Sarandon, who looks about as ready for a rest home as Edward Norton does.

Brady tricks Bill into returning to their Little Dixie, Oklahoma, hometown, where he tricks his unsuspecting brother into a dubious scheme involving a Jewish drug tycoon and redneck criminals. The only real reason for Bill to stay past an hour is the suggestive manner of a local poet/schoolteacher (Keri Russell).

Dead bodies pile everywhere by the time the dust settles, although none of these deaths is exactly funny. Stupidity compounds itself as every character follows a bad decision with a worse one. The final scene indicates that Nelson simply ran out of ideas for moronic behavior instead of finding an ending.

Jewish characters played by Richard Dreyfuss and Josh Pais come uncomfortably close to anti-Semitic portraits. But then the backwoods yokels (especially one played by Nelson himself), Southern lawmen and Ivy League snobs don't fair any better, so you assume Nelson is struggling to play with stereotypes and making a botch of it.

For an actor-director, Nelson certainly allows his cast to run amok with cartoonish performances. It's a good thing many scenes take place outdoors, where scenery is not so easily chewed.

The direction is sloppy and scenes often indifferently framed, which is surprising from a filmmaker who has shown himself capable of better. The Shreveport, Louisiana, production looks OK -- but just OK.