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 it's actually the executive producer, hiding to see if directors Bobby Farrelly and Peter Farrelly would notice. They didn't.
Matt Damon met his future wife Luciana Damon when the cast and crew dragged him out one night to a bar, where she happened to be the bartender.
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.
Ben Carson is a real-life surgeon 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 appear in the hospital waiting room.
When Cher first signed on to do the movie, the character in the script she was supposed to play just said "actress". Directors Bobby Farrelly and Peter Farrelly thought it would be a cool idea if Cher just played herself, and so they changed it.