Continuity mistake: When they tape Percy's mouth shut before putting him in the restraint room, the handkerchief is partly outside his mouth and gets stuck to the tape, when they let Percy out, the handkerchief has moved. If he's been locked in there with the straight jacket on, there is no way he could have moved it.
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.