During a montage that shows the passing of several days, Sylvia Sidney is wearing the same dress the entire time.
When a stone is thrown through the window at the jail house, the sheriff goes over to check it out. There are bars on the window when he first looks out; after they pan back from the people outside, the bars are no longer on the window.
When Joe is shown standing looking into a flower shop window, imagining his future life without Katherine, he turns around; the next shot shows him standing in front of a haberdashery.
In the train station, when Katherine closes her suitcase after removing the needle & thread so she can sew Joe's coat, a small bit of cloth remains visible. In a next shot, she finishes sewing the coat, but the small bit of cloth has disappeared.
When Joe is listening to Katherine's testimony, the filaments of the radio's tubes (visible thru the open back of the radio) are not lit, indicating no power to the radio, yet the broadcast can be heard.
A newspaper headline features the misspelled word 'Kidnapers'.
When the newsreel of the attempted lynching is run during the trial scene, the frame of the newsreel is frozen several times, in order to show the defendants as having taken part in the crime. But while the newsreel projector is supposed to have stopped, the ticking of the projector continues in the background, as if the film were still running.