SOMEONE should have told the brothers Farrelly, creators of beyond the pale gross-out comedy classics, that once you're on to a good thing, stop, repeat, and reap the box office rewards.

As much as I would have liked to have been offended by any of their back catalogue, which includes There's Something About Mary, Shallow Hal and the historic Kingpin, I've simply been laughing too hard to even begin to get irate.

Sadly, their new "let's take a weirdness and exploit it for comedy" vehicle is a turn away from the path of puerile and hilarious set pieces, and a wander down sentiment alley. Oh yes, the men who saw no problem in using multiple personalities for laughs, and zipping up Ben Stiller's most personal part in Mary, have gone all mushy on us. And it just doesn't work.

Matt Damon and Greg Kinnear play Bob and Walt, Siamese twins from Martha's Vineyard, who make a great living with their Quickee Burger restaurant, knocking out meals in three minutes for the sympathetic locals, who'll step up to the plate if anyone dare use the "freak" word.

Despite being an introvert and extrovert respectively - Bob e-mails his internet girlfriend, while Walt simultaneously "entertains" a lady - they're happy to be literally joined at the hip.

But Walt has a yearning to be an actor, and so off the brothers go to LA to see if they can make as actors on TV.

Crossing the path of the ruthless Cher, who sees their embarrassment potential and wants to sabotage the rubbish show she's contracted to, they end up as the new "star" of Honey and the Beez, where Walt acts and Bob hyperventilates with stage fright behind him.

All of which is absolutely fine, except that it's not either funny or gross, the two main attributes which fans of the Farrellys will want to see up on screen.

Yes, the two lead men play their parts very well, with a lovely chemistry and a great physicality which makes the most of the comic situations their bodies place them in, but they can't redeem the preachy quality of the whole proceedings, or its lack of laughs.

An audience will find it hard to escape the feeling that this disability has simply been plucked as a film idea because of its comedy potential - "oh, let's think how Siamese twins would play sport, chat people up in bars", etc - and yet this contradicts the message of the film. It says "let's accept these people", but then cannot resist the temptation to set them up for mockery.

Even Meryl Streep, gamely popping up in a cameo role towards the end, cannot save proceedings. They should have gone from dumb to dumber to even dumber, not schmaltzier.

Two heads may be better than one for the brothers in the film, but the real life duo better get back on track.