Despite the shared liver and nine inches of flesh on their sides that keep them together, the two have long agreed not to old each other back, and surgery is out of the question since it could be dangerous to Walt. Thus, Bob agrees to move to Hollywood with Walt so that he can try to make it in the movies.

After repeated rejections, they run into lingerie model and aspiring actress April Mercedes (EVA MENDES) who introduces the two to her agent, Morty O'Reilly (SEYMOUR CASSEL), who takes on Walt as his client.

The first job he finds for Walt is a bust, but he and Bob accidentally run into Cher (CHER) who isn't happy with her new TV show. With final say on who's cast as her co-star, she chooses Walt knowing full well that the network will cancel the show when they learn about his condition.

They don't, however, and the show becomes a surprise hit, propelling Walt into stardom. Bob, however, feels like little more than a gimmick, a point he tries to keep secret from May Fong (WEN YANN SHIH), his Internet girlfriend who lives nearby.

With their physical condition increasingly getting in their way, Bob and Walt must decide whether to go on living as they always have or take the physical and emotional risk of being surgically separated.

Kids -- and adults -- marveled at the thought of living that way, and those who understood the mechanics of reproduction wondered how the two fathered twenty-two children between them, while joined together and obviously lacking privacy.

The film "Stuck on You," featuring Greg Kinnear and Matt Damon as similarly conjoined twins, briefly touches on that subject, but doesn't delve long or in much detail regarding that. That's probably somewhat due to having to adhere to the "constraints" of a PG-13 rating.

Nevertheless, it's rather surprising considering that the film comes from Peter and Bobby Farrelly, the filmmaking siblings probably best known for the flinging of a certain male bodily fluid, ah, hair gel in "There's Something About Mary."

Like parts of that and their other films, the siblings like to showcase various characters -- who are underdogs and/or different from the "norm" -- in something of a loving, us vs. them fashion. That is, as mixed with crude, sophomoric and occasionally hilarious supplemental material.

Unfortunately, much of the latter is missing in this effort that, not surprisingly, plays out like a comedy skit elongated to feature length. Notwithstanding whether the film is insensitive to those who live with the same condition (along with their family and friends), the effort simply isn't that funny, even in its politically incorrect but friendly fashion.

Considering the subject matter, there are two possible routes to take. One would be to throw all p.c. caution to the wind and sail full steam into the dangerous seas of black comedy. There are tinges of that here, particularly in regards to the various physical sight gags. Those come in both the predictable and unexpected variety and I have to admit that a few of them are humorous.

Yet, the Farrellys seem more interested in trying to make something of a more substantial version of their usual touchy-feely material. There's certainly nothing wrong with that as long as it works and doesn't drop speed bumps along the route of the second possible path.

Unfortunately, and in respective terms, it doesn't and does. The charming and/or sympathetic moments fall short, while the road toward an imaginative, smart and witty satire on people's perceptions of others and themselves is pitted with too many plot-holes and some indecisive drivers who can't decide what lane to be in.

All of which results in a rather flat comedy. You know you're supposed to root for the conjoined protagonists and laugh with them and their physical hindrances and abilities. Yet, the way in which everything plays out hinders a great deal of that.

While Damon ("The Bourne Identity," "Ocean's Eleven") and Kinnear ("Auto Focus," "We Were Soldiers") don't remotely look like twins - a point explained by their shared liver aging Kinnear's character faster than Damon's - the actors are actually fine in the roles. We're not talking award-caliber performances, but they're certainly the best thing the film has to offer.

Eva Mendes ("Once Upon a Time in Mexico," "2 Fast 2 Furious"), however, is apparently present to showcase her abundant cleavage, Seymour Cassel ("Stealing Harvard," "The Royal Tenenbaums") to don a purposefully bad rug up top, and Wen Yann Shih (making her feature debut) to be the "straight man" to the various shenanigans. Cher ("Tea With Mussolini," "Mask") and, of all people, Meryl Streep ("The Hours," "Adaptation") are also present, playing versions of themselves.

While Cher pokes fun at her diva personality (although not to any tremendously laugh out loud extent), the brothers must have had something on Streep to get her to appear here. That's especially true since her role is so underdeveloped (although she gets to dance in a musical stage number about Bonnie and Clyde). That last bit might sound a bit like "Springtime for Hitler," but it fails to live up to the expectations surrounding it, much like the rest of the film.

With their hearts in the right place but their funny-bones mysteriously weaker than usual, the Farrelly brothers might have the right intention with this effort. It's just too bad it isn't funnier, charming and/or as heartwarming as obviously intended. "Stuck on You" never manages to stick and thus rates as just a 4 out of 10.