Continuity mistake: When Warden Ranken first goes to see Manny in his cell, he is walking down a prison corridor with prison cells on the left side of the camera and the prison wall on the other side. And when he is coming back from Manny's cell, he is coming down the same corridor. The problem is only that he is going the same direction as he was when he was going TO Manny's cell.
Continuity mistake: Towards the end of the film, in the control room, as the guys are arguing about what to do, the man sitting at the computer terminal is wearing a sweater over his shirt and a black watch. The older man says something, then goes over to the terminal, but now the guy's sweater is off and his watch is in front of him on the desk.
Continuity mistake: During the freight train scene, the runaway passes the same set of gondola cars twice.
Revealing mistake: When Manny goes to lay down and uncouple the two locos at the end, a 7" icicle is flapping in the breeze.
Answer: It wouldn't derail, it would break the bolt on points - the part of switch that moves, causing the points.