When Evil Roy Slade realizes he has the short cowboy's hat on, he grabs the hat and starts to take it off. Then when the short cowboy hands Evil Roy the correct hat, Evil Roy still has the short cowboy's hat on.
Harry Fern's cash register contains modern currency, 1s 5s and 10s.
The psychiatrist uses ink blots (also called the "Rorschach" test) with Slade. These were not developed until the 1920s, well after the period depicted here.