Factual error: Tom Hanks refers to an Intensive Care Unit, and although a few physicians had already discovered the practice of separating the sickest patients into a separate ward in the 1930's, the term Intensive Care Unit was not yet in use.
Factual error: This movie is set in 1935. Back then, executions were done by hanging. The Louisiana Legislature changed the method from hanging to electrocution in 1940.
Continuity mistake: When William "Wild Bill" Wharton spits the Moon pie into Brutus "Brutal" Howell's face you can see that the Moon pie lands on his shirt, tie, lapels of his coat and on the right shoulder of his coat. In the next shot when Brutal and Paul throw Wharton into the padded room, you can see that the right shoulder of Brutal's coat is completely clean, but the Moon pie is still on his shirt, tie and lapels. (01:20:58)
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.
Factual error: When Paul returns home, his wife asks him what the doctor said. He replies "...gobbledygook mostly." The trouble is, the word "gobbledygook" wasn't coined until 1944. This scene takes place in 1935.
Continuity mistake: Roll on 1 means to crank up the generator all the way. On top of the machine are light bulbs that all light up when the generator is turned up. However, when they are executing Del they have a sideshot of Brutus and you can see the lightbulbs all lit up, but Percy hasn't said Roll on 1 yet. (01:37:00)
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.
Factual error: The cell keys carried by the guards do not date to 1935.
Continuity mistake: The guards take John to see the Fred Astaire movie and John sits well to the right of centre in the theatre. We see John mesmerized by the movie, Paul sitting a row behind in the centre of the seat theatre and the light from the projector spreads wide directly behind and over top of Paul's head. Yet, when we see John again a moment later, when he's says "They's just like angels", the projector light is directly behind John, deliberately giving the illusion of a halo. This would not occur as shown unless John had moved over to the centre of the theatre.
Other mistake: The death warrant for "Arlen Bitterbuck" is dated 1935 but the subtitle in German says 1985. (00:25:15)
Continuity mistake: When John Coffey grabs Percy by the throat, Percy pulls out his night stick and drops it on the floor. A long leather strap can be seen attached to the handle. But after John lets him go, the long leather strap can be seen dangling on Percy's right side, when it should be still lying on the floor with the night stick outside of Coffey's cell.