Character mistake: You'd think prison guards on Death Row would have known a little more about safe restraints, the way they bind and gag Percy could eventually kill him. They stuff a handkerchief all the way into his mouth, then tape his mouth closed. The gag reflex could suck the handkerchief into his windpipe and suffocate him in about three or four minutes. Even if he might be able to find away around the danger of suffocation the fact remains that no trained, experienced prison guard is ever going to restrain someone in that way.
Suggested correction: Not everyone even has a gag reflex, and it is easy, though not comfortable to push the handkerchief forward into the mouth with the tongue. You can see Percy breathing through his nose, so he's not running out of air. The other guards had no intention of leaving him in the cell for a long time, only long enough to teach him a lesson.
It doesn't matter what he "might" be able to do, or even if he could push the handkerchief forward. That's not the mistake. A trained, experienced prison guard would not restrain someone like that. Never.
Again, what might or might not have happened is irrelevant. No skilled, trained, experienced prison guard would apply a gag in this way.
Character mistake: The Fifth Amendment Double Jeopardy Clause does not apply. Libby could be convicted of 1st Degree murder when she gets out and pursues Nick. It doesn't really matter to the plot, however, because it was what Libby believed to be true and motivated her. Further, she ends up shooting Nick in self-defense. So it's all good.
Character mistake: Thomas rips off his one glove as he makes his escape but then grips the bottom edge of the security door to slide under it. Smooth metal door would leave perfect finger and palm prints. I doubt detectives would miss prints on a door that was normally recessed away from the public. His prints may not be on file but would be easy to obtain once he was under suspicion. (00:19:20)