At the beginning of the movie, when the twins are getting out of bed, there is a shot that shows their feet on the floor and there appears to be a face under the bed. It's rumored to be baseball equipment, but is actually the executive producer, hiding to see if directors Bobby and Peter Farrelly would notice. They didn't.
Matt Damon met his future wife Luciana Barroso when the cast and crew dragged him out one night to a bar which happened to be where his future wife was the bartender.
Ben Carson is an actual doctor who has successfully separated conjoined twins in real life. In a 22-hour surgery, he was the first doctor in history to accomplish this task with both of the twins surviving. His wife and three children also appear in the hospital waiting room.
Ray "Rocket" Valliere's speech following the credits was not planned. He rambled on while the cameras kept rolling. Lunch had already been called and the crew was restless. But his speech was so heartfelt that no one stopped him.
When Cher first signed on to do the movie, the character in the script she was supposed to play just said "actress". Writers and directors Bobby and Peter Farrelly thought it would be a cool idea if Cher just played herself, and so they changed it.
The country song played over the closing credits is sung by George Schappell, one of a set of conjoined twins who is mentioned in the film.
Tom Brady makes a cameo as a film crew assistant. He is the one full of facial piercings laughing at Cher's computer generated bubble butt.
Jim Carrey was once attached to this film, with Woody Allen in talks to play the other brother.
The surgeon Ben Carson in the film (billed as Benjamin Carson, Jr.) was 2016 Presidential candidate Ben Carson.
When the twins first meet Mrs. Streep in the restaurant they say that they're friends with Timothy Sheehan. Timothy Sheehan was Greg Kinnear's assistant while filming this movie.
Ben Carson, the surgeon who separates Walt and Bob, is the subject of a biopic starring Cuba Gooding, Jr. The movie is Gifted Hands: The Ben Carson Story (2009).
During the high school football flashback, former NFL star Ricky Williams had a cameo as a coach.
In the homecoming game scene, the twins trounce the Nantucket Whalers while playing for the Martha's Vineyard Vineyarders. There is a very close rivalry between both high school football teams and many people from Martha's Vineyard were delighted to see the Whalers lose on film. Nantucket had no comment.
The unique way in which Greg Kinnear sings "Summertime" near the end of the movie is a very close imitation of the way late soul singer Billy Stewart sang the song on his "Unbelievable" album, released in 1966.
Cher has a copy of People Magazine's "Who's Hot Who's Not" edition. The cover's "Hot" members features Cher along with previous Farrelly Brothers film collaborators Cameron Diaz, Chris Cooper, Renée Zellweger, and Gwyneth Paltrow. The only person listed as "Not Hot" is long time Hollywood Property Master Richard K. Wright.
Just to be technical, conjoined twins are always identical. During the final division of cells when a healthy set of identical twins becomes the end result, for twins who remain conjoined, this division process is incomplete and they develop in the womb joined in some way.
The directors wanted April to have huge breasts to emphasize on her bimbo character and were considering having the actress wear a prostethic pair. But upon meeting Eva Mendes, they rewrote the role after telling her she had "great breasts".
Dane Cook filmed a scene as an LAPD officer who pulls over Bob and Walt, but was cut from the final film. His scene can be seen in the supplemental section of the DVD.
This was the Farelly Brothers first movie to be Filmed in Panavision (anamorphic) 2.39:1, a format favored by DP Dan Mindel.
Much of the comedy pertaining to Siamese twins/separated Siamese twins has a similarity to a sketch on Season 3 of the late 90's HBO sketch comedy Mr. Show
It's pretty obvious that the hairstyles and clothing designs for Walt and Bob are the same ripped directly from the Farrelly brothers other movie duo of Harry Dunne (Jeff Daniels) and Lloyd Christmas. Noticeably, the long blonde hair and the brown bowl cut.
During Bob's and May's first date, Walt referenced "...that Woody Allen movie? I think it was, uh, 'Annie Hall' (1977) where the guy goes out with the girl and to try and ease the tension he suggests they kiss at the beginning of the date instead of the end?" Matt Damon made the same suggestion to Minnie Driver in 'Good Will Hunting' (1997).