Jack Black, meanwhile, the Farrellys had seen in High Fidelity, and realised he had exactly the right everyday qualities for the part. “After screening the film,” says Bradley Thomas, the brothers’ regular producer, “we realised Jack was everything we needed for Hal – he was fresh and had this incredible ‘likability factor’ and energy that were essential for the role. And he is very, very funny.”

Plus he was, well, rather ordinary looking, adds Bobby Farrelly, pointing out that you would genuinely dislike a good-looking guy who behaved the way Hal did (which is the way an awful lot of good-looking guys behave, especially in movies). “When an average-looking guy is depicted as shallow,” explains Bobby, “at least you say, ‘Well, he has no right to be that shallow.’ So we felt audiences would look more favourably at this flaw in a guy who was more of an ‘everyman’ type.”

Black - whose other credits include Saving Silverman and Jesus’ Son and will soon be seen in Orange County - had never played a leading role before, and was especially nervous about starring opposite Paltrow. So he insisted on auditioning for the part. The Farrellys wanted to give it to him anyway, triggering off a bizarre stand-off in which the actor wanted to test for the part and the directors wanted to cast him without an audition. As in most things, the Farrellys won, although Peter did concede that Black was scared he “was about to bust, going up against such a powerhouse” of an actress.

Fraternal greetings - Shallow Hal star Jack Black with Bobby (left) and Peter Farrelly.

Also in the movie are Seinfeld star Jason Alexander as Hal’s pal, Mauricio, who is even more obsessed with physical beauty in his dates than his friend. For example, he breaks it off with one girl because one of her toes is too long. And then there is Rene Kirby, a non-professional who plays Hal’s friend, Walt. Kirby suffers from spina bifida, and goes through life on all fours. Very successfully, I might add: he is a first-class skier, a prize-winning gymnast and holds down a top job with IBM. But he can’t walk, and the Farrellys felt that the almost casual inclusion of his character as Hal’s best friend would bring home even more effectively the basic theme of the movie: that you shouldn’t judge people by the way they look.

“I think Shallow Hal is an important film for Peter and Bobby,” says Thomas. “Their jokes are as funny as ever, but this time they’re a bonus. There is a strong message behind the story about seeing inner beauty, when everything in today’s society is so focused on the superficial. The movie is like an old-fashioned love story, and the relationship between Hal and Rosemary is really the spine of the film.”

“Peter always said we hadn’t made our best movie yet because, while we’d made people laugh, we hadn’t made them laugh and cry,” says Bobby. “Shallow Hal is our most emotional film. We wanted to make people think and go through a range of emotions as well as laugh. And I think we’ve accomplished that.”

“I’m proud of all of our movies,” sums up Peter. “But this one’s a little more ambitious.”