Tip Corey uses a nail to carve a circle on the side of the McCain barn to demonstrate his "throw the knife/shoot the gun" trick for Mark. When he's told to leave and retrieves the knife from the barn, the circle is gone.
Unlike almost every other western ever made. When the two men face off. The townspeople stand directly behind Sammy Davis's character. And this gun fight is particularly dangerous for bystanders. McCain's rifle slugs would pass right through his target and hit bystanders. The bystanders don't even seem to flinch once the shooting starts. All of this goes against human nature.