Continuity mistake: After Pierce Brosnan does the deal for the bullet, Anjelica Huston rides off with his horse attached to her carriage. Only problem is we see the entire exchange, and at no point does anyone tie the horse on.
Continuity mistake: Gideon hitches his horse behind a bush at the railway camp. The horse doesn't have a brand on its left rear. When the railroad foreman sees the horse, he recognises it because of a large letter 'M' stamped on the horse's flesh.