Whether caused by staining or decay, the condition of Doc Council's teeth is poor, though it varies throughout the film. At one point his teeth become miraculously and uncharacteristically white (the condition of actor George Kennedy's real teeth).
Appleyard's "glass eye" moves with his other eye. Glass eyes don't move as they are not attached to anything.
When Homer Grindstaff is supposed to be locking the bank door early in the movie, the key is clearly not even in the lock. He is merely making a gesture by fiddling with the key.
When "Doc" Council stands over Junior and shoots him, his shotgun doesn't kick even one inch. Holding it like he did the gun should have kicked back quite hard.
As Appleyard (Stewart) is looking out the train window at Council (Kennedy) the window changes to that of a modern train car. The window is double paned glass that has a leak in it and is fogged up in the upper left portion of it. In the following scenes it changes back to a period railcar window with single pane glass.
In the closing scene and credits, the vehicles crossing the bridge over the railroad track are correct older vintage cars. However, on the second bridge in the distance, new cars can be seen crossing.
When the conductor is confessing his role in the plot to Mattie, a moving shadow of the boom microphone is visible on the wall of the coach behind him.