In the final courtroom scene just before the prosecutor, Will Geer's character, is quoting from the Bible, he grabbed his eyeglasses and quickly put them on his face. They obviously did not cover his eyes. Geer was not looking through his glasses but instead his eyes were looking below the lenses.
Perry tells phones Reverend Post that he is at the bus station in Kansas City, Missouri. Post replies "You've already broken parole by quitting your job. You'll break it again if you step into Kansas. Whatever you do, don't cross that river into Kansas." However, the state line at Kansas City is a land boundary that is near the Kansas River, but is neither that nor the Missouri River.
When Alvin Dewey comes into a room full of reporters, Jensen is leaning against a doorway. He pulls a pack of cigarettes pack out of his jacket, takes a cigarette out of the pack and puts it to his lips and lights it. After taking a puff, he puts his lighter and cigarette pack back in his jacket pocket. Then he turns to listen to Dewey. In the next scene Jensen is turned 90 degrees to where he was in the previous scene with the pack of cigarettes in his left hand lighting his cigarette again.
When Perry and Dick arrive at Clutter's Place, still sitting in the car, Perry says: "Let's pull outta here". Then Dick drinks from his bottle. Later in the movie, when Perry makes his confession, we see the same scene, but now Dick drinks before Perry says: "Let's pull outta here"
At the beginning of the movie, after Dick has picked Perry up from the Kansas City bus depot and both are crossing the river into Kansas, the process is running in reverse, giving the impression the car is suddenly moving in reverse despite the two immediate shots bookending this one clearly shows the car moving forward.