Revealing mistake: While Julius is talking to the man in front of the lingerie store on Hollywood Blvd, when the man's partner rides up on a motorcycle and tries to snatch the suitcase, we can see the stunt wire carabiner attached to the back of his jacket as he flies off. (00:12:30)
Visible crew/equipment: When Arnold throws one of the Clane brothers into the elevator, you can clearly see the cable that pulls him backwards. (00:23:49)
Factual error: When Arnie and Devito are stealing the car and Devito sets off the car alarm, Arnold picks up the car from the back end to stop it. If you watch the wheels you will notice that they don't shake or move at all when Arnold sets the car back down on the ground. (00:27:23)
Visible crew/equipment: When Julius enters the supermarket parking lot, in the long shot we can see the stunt ramp used to lift the driver's side of the car, to go into ski mode. In this and following long shots of the stunt, we can also see the window roll cage bar directly behind the front windshield (the obvious stunt driver grips the roll bar with his left hand and steers with his right hand), as well as the top of the seat supports behind the front headrests. (00:30:55)
Continuity mistake: In the scene where Danny and Arnold are eating the "nuked" food. You can see the amount of milk Arnold has in his glass changes. He actually has more at the end of the scene. (00:36:36)
Other mistake: When Devito sends Arnold into the house to get his stuff and go with him to New Mexico and Houston, Devito quickly jumps into the car to drive off. (You can see on the long street behind him that there are no cars coming). Yet, not one second has gone by and you are looking at him from the front of the car and Linda and her sister pull up behind him blocking him in the driveway. They turned in from the left which was the same stretch of street you were looking at with no cars on it just one moment earlier. (00:48:40)
Continuity mistake: Arnie & DeVito are walking through a crowd with their white coats hanging over their shoulders, black sunglasses and hawaiian shirts on (DeVito is teaching Arnie how to act semi-normal). If you look in the near background you can see a few extras that walk across right behind them about seven or eight times, they were obviously told to walk closely across behind the two stars and then turn around and walk closely across behind them again and again and again. You would think that a movie with such a huge budget would be able to hire a few more extras to do that job.... (01:04:13)
Continuity mistake: There is a scene where Arnie and Danny DeVito are in the washroom of a nightclub. In one shot there is a beer bottle on top of a paper towel dispenser, and in the next shot it's on the other paper towel dispenser. (01:11:15)
Continuity mistake: In the final scenes, the twins have had their own sets of twins. Both appear to be boy/girl twins as there are 2 in blue and 2 in what appears to be pale pink. As they walk towards the mums they are arranged boy on the left of our screen in both buggies/strollers, but when they are taken out the babies in Schwarzenegger's buggy have changed round as the baby in blue is lifted from what would be the right side. (01:40:00 - 01:45:00)
Audio problem: In the bar scene where the twins are dancing with the girls, keep an eye on the band in the back. The singer and the guitarist are not always singing and playing in time with the music. Most visible at the end of the scene, the music has the guitar playing a long riff and no vocals, yet the guitarist is barely moving, and the singer is singing with emotion.
Continuity mistake: Arnie enters the parking lot driving on two wheels crying "Woooa." The close shots show him with one hand on the wheel and the other outside on the window; but on the wide shots, with the stunt, both hands are inside and his mouth closed but still the cry is heard. This mistake goes on every time angle changes.
Other mistake: When Julius visits the orphanage where Vincent grew up, he begins to talk to the nun about the bed where Vincent slept and how it was near the fire extinguisher and alarm. While talking about it, he makes a motion as though he is pulling the fire alarm, but doesn't actually do so. As Julius and the nun are exiting the room, the alarm pull handle falls down on its own (no alarm goes off).
Audio problem: When Vincent is receiving the parking ticket for being in the handicap spot, at one point we hear him say "Handicap my ass" but his mouth is not moving. Clearly dubbed in later.
Continuity mistake: At the end of the film, when they are at the fair with their own "Twins" Danny is holding his children and the one in his left arm is crying while the one in the right is not. When the snapshot is taken and the picture shows the still shot, the crying baby is now lethargic while the other is crying instead.
Continuity mistake: When Arnold kicks down Mitchell Traven's door, you can see the hinge intact at the top right of the door frame. When the camera faces Mitchell Traven, then Julius, you can see the door frame again and the hinge is damaged.
Continuity mistake: At the bar, when the four are sitting at the table, the amount of beer in the glasses and pitcher change between shots, as does the position of the pitcher.
Chosen answer: Although I wouldn't call one a bad guy, Professor Werner is the the one who raised Julius, and would remain a friend because of this bond. Mary Ann (the twins' mother) however, was told that Julius died at birth and was never told about Vincent. She blames Professor Traven for this (probably since he's the only one around to yell at). Vincent on the other hand was never told his mother died during childbirth and he grew up thinking his mother abandoned him. Until Julius showed up, he never knew he was part of an experiment and he had no knowledge of either doctors and probably no feelings regarding either of them.
Bishop73