Revealing mistake: In the final scene as Doc tell Billy good-bye if you look up to the top right hand corner of the screen you can clearly see a jet trail in the blue sky. Certainly not possible in those days. (01:42:20)
Revealing mistake: There is a scene where one of them jumps on a horse, and you can see one of the crew holding on to the reigns as the horse throws its head back.
Chosen answer: He may have. When Billy started whistling, the bounty hunter's face changes. He continues to speak to Billy in a dismissive tone, but does eventually pull the trigger (although Billy had unloaded the pistol). Hard to believe he would just shoot some mouthy kid in a bar.