Continuity mistake: Arnold goes to the gay bar to solicit the help of the guy he saved at the beginning of the movie. The guy is wearing a white shirt and a vest black/gold lamay. During their conversation he takes off the vest, then it cuts to another bartender. When it cuts back the guy has the vest on, another shot and the vest is off again. (00:08:05 - 01:10:50)
Other mistake: If the bullets from the super gun move at just under the speed of light, how come the bad guys can't hit him or the girl? The bullets would arrive almost instantaneously and that would mean minimal compensation for them running. Plus the guy had them locked on when he shot.
Factual error: Even aside from the ridiculous recoil that a railgun would cause (yeah, I know they don't use gunpowder, but there's got to be SOME opposite movement, surely), how come when the darts (bullets, whatever) go straight through people, they still get thrown backwards? The passage straight through them means minimal energy being transferred to them, and as such they shouldn't be hurled backwards that much.
Continuity mistake: When Arnold gives the girl a credit card, he slides the card to give her credit, but the magnetic strip is facing the wrong way. (00:36:50)
Continuity mistake: At the end, right before the train crashes into the limo, the back of the limo is facing the blocking rail. However, after the train hits the limo, the front half of the car is right next to the rail, and the rear half is nowhere to be seen. (01:48:30)
Continuity mistake: Arnold dives to save the girl under the lid of a fridge. When all the drill bits are shot at him with his hand above the fridge door, none hit his hand. But in the next angle one penetrated his hand. Then in the next scene, when he's driving the van with both hands and when he swipes the credit card the wound appears and disappears. (00:28:30)
Factual error: When the bad guys are looking through walls with the rail gun's scope the light on the gun shines through the wall, but in real life it doesn't do that unless you are looking through a window. (00:27:15)
Continuity mistake: After the court scene, when Arnold and Vanessa are making their exit toward the van, they get in, the van explodes and the camera pans to the underside of the van, showing Arnold pulling a manhole cover closed. The manhole cover was not there when they showed the van from a distance and they didn't have enough time to get in the van and escape through the bottom. Also, because several seconds passed before he closed the manhole cover you would have to assume he was still above ground when the bomb went off, therefore killing him. (01:46:20)
Continuity mistake: When Arnold is hanging under the parachute the plane tries to hit him and he shoots at the plane, breaking the glass of the cockpit windows. When the plane lands later on, the windows are intact again. (00:56:25 - 00:58:15)
Revealing mistake: When Arnie jumps from the plane, notice the stunt double. He weighs about half of what Arnie would, and has no muscles. (00:55:10)
Plot hole: There's absolutely no reason why Kruger had to page Lee from the plane after he'd been drugged. The bad guys had no idea where Lee was until he did that and they traced the phone call. Not only did Kruger give away Lee's location, but he also gave away the only thing keeping the bad guys from killing him.
Revealing mistake: When Arnold is in the plane and throws his belt buckle-knife at the traitor. The next shot shows that it bounces off and continues to spin. Pretty obvious that it's held up by a wire. (00:53:10)
Visible crew/equipment: When the warehouse has collapsed on Arnold and he is coming out from underneath the rubble, you can see a guy "hidden" behind some tubes, wearing protective eye wear and holding a welding rod to make a shower of sparks (he is only visible in the widescreen DVD version). (01:34:30)
Factual error: In several scenes where someone is shot with an EM gun it nails them to the wall, but if someone was shot with a bullet that was going near the speed of light it would go right though them. And the person wouldn't move at all, they would just fall down.
Factual error: When the glass shutters come down in the Cyrez building, both he and James Caans' character start shooting at the glass. Bullet proof or not, you would be able to see marks on the glass. (01:24:00)