Continuity mistake: When Buster is shot, his hat with the hole in it disappears.
Continuity mistake: When Buster approaches the table, we see the glass is about 1/3 full. Next shot it's 2/3 full. Then it's picked up by the chap with the goatee, But it reappears on the table at "weapon." Next, at the wide shot, it's empty, (as are all the glasses, also the other glasses were full, now they are empty).
Continuity mistake: In the saloon scene, Buster sits at the table, then later stands up. He is right next to the table. Then we see a wider side shot, where he and his chair have teleported away from the table. He does his kicks then he is back close by the table again.
Factual error: When Buster joins the card game in the saloon, he looks at the hand of the player that had just left. Given the circumstances in the saloon, the cards cannot be spot clean and white as fresh snow. Also, they seem to be plastic cards, which did not exist yet back then.
