Corrected entry: Conjoined twins are always identical twins (occasional exceptions where facial deformities are present (e.g. in some twins joined at the skull), which is not the case for the twins in the movie). These are not identical twins (Greg Kinnear is also over 7 years older than Matt Damon). See Conjoined FAQ, Twins Operation, and Twins. You will see photo after photo of identical faces.
Corrected entry: Towards the end of the film in Bobs restaurant, Mimmy asks Bob if her and Rocket can leave early tonight. The clock on the wall behind Bob reads a quarter past one but from looking out the windows there is clear daylight coming through.
Correction: Quarter past one in the afternoon, just after lunch. It's daylight then.
Corrected entry: I highly doubt they'd be able to shut the jail door with the twins growth in it. I don't know a lot about livers, but I think they're thicker than paper. (01:20:05)
Correction: There is enough space between the bars in the door to accommodate the join between the two bodies. There is a space between the last bar of the door and the wall of the cell.
Corrected entry: When the twins are on the way to the hospital and Morty appears on his scooter, you can see the smoke of the cigar going upwards while it should be going backwards because of the speed.
Corrected entry: When the boys first lay out the buns on the "tester" at the beginning of the film they put down 4 columns of 3 buns each. When the scene shifts back to them the have 3 columns of 4 buns each. (00:03:25)
Corrected entry: In the scene where Cher takes a break during filming, she hands a bottle to her personal assistant. The bottle changes from Pepsi, to mineral water, to Pepsi.
Correction: While the assistant does alternate between Pepsi and mineral water, that isn't a mistake. It just means that she is carrying two bottles. The scene where she does this is just one shot meaning there would be two bottles there anyway. With how volatile Cher was and the assistant constantly trying to please her, it makes sense she would bring around two drinks for her.
Corrected entry: In the scene at a diner in LA the twins start talking about getting an operation to be separated. One of them starts smoking. This happens again in a strip club later that night. In CA it is illegal to smoke indoors and is highly enforced. There is no way the waitress or the strippers would just keep doing their jobs without telling him he can't smoke.
Correction: Apparently its not highly enforced if many pool halls, and other various business establishments allow smoking indoors.
Corrected entry: In the scene where May is feeding Bob soup because he says he does not feel well, she leaves and he says, "Bye Wen," which is the actors real name, not the characters.
Correction: She actually says, "Bye then."
Corrected entry: In the scene at the end of the film where Walt and Meryl Streep star in Bonnie and Clyde, watch as Clyde/Walt sings the song ... various parts of it are terribly out of sync.
Correction: We can assume that Walt is lip syncing in the play, so that would make it a character mistake.
Corrected entry: When the boys are arriving at Bob's girlfriends apartment they open both car doors and exit through the passenger side, leaving the driver side door open, never closing it. When they get back in the car, the driver side door is now closed.
Correction: If you listen closely, you can hear that Walt gently shuts the door.
Corrected entry: When May first comes to the hotel and wakes the guy at the desk he starts typing. The scene cuts and you can see that there is nothing on the page that he just typed on. (00:37:00)
Correction: Maybe the ribbon was dead, he was just faking it anyway.
Corrected entry: At the beginning, when the clock goes off, the very next shot shows the bed and the floor. Then there are 2 sets of feet hitting the floor. If you look under the bed, you can see a man's face, like he's laying under the bed, looking out at you.
Correction: Actually it isn't a crew member it is just baseball equipment that looks like a face staring at you.
Corrected entry: I really doubt a police officer would high-five anybody behind bars. (01:20:45)
Correction: This is an opinion, not a mistake. Anyway, the high five was done for comedy, not realism.
Corrected entry: Just before Walt enters the theater to get ready for his role in "Bonnie and Clyde: the Musical", he has his usual haircut. But from then on his hair becomes shorter and darker.
Correction: During the show his wore a wig for his character.
Corrected entry: In the operating room, Matt Damon and Greg Kinnear are in the opposite beds they should be after being separated. There isn't enough space in the room to have switched the positions of the beds, and in their present condition the twins couldn't have gotten up and switched places.
Correction: Walt and Bob are only shown in the operating room before the separation. When the girls see them, they are in a recovery room. Plenty of time to move the beds down the hall and onto different sides.
Corrected entry: In the opening scene where Bob and Walt are lying in bed, there is a person's head visible under the bed.
Correction: According to the Farrelly's DVD commentary, nobody was under the bed. They don't know what it is but it is certainly not a person.
Corrected entry: When Bob and Walt walk past the four singers wearing sunglasses on the boardwalk, the one on the far right appears to be a heavily made-up Ben Stiller.
Correction: It's not Ben Stiller. IMDb lists Otis Walter Albert, Elizardo Del Rio, and Robert F Smith as the "Outta Sight Singers".
Correction: There is a part where Kinnear reveals he is growing old at a faster rate then Damon because Damon has most of their liver. This is presumably why they don't look exactly alike.