Other mistake: Johnny Brown is serenading Molly in the meadow as she sits up on the branch of a tree. In shots where we are looking down on Johnny (from over Molly's shoulder), the shadow of the canopy that protects the actors from the sun can be seen as a perfectly straight line on the ground, behind Johnny. The shaded/unshaded areas move as the canopy shifts in the breeze.
Other mistake: In the final gunfight when Joe shoots the gun from Ramon's hands and kills the rest of his gang, he fires six shots. He then shoots the rope that Silvanito has been tied up to without reloading. His gun is a revolver, which only holds six bullets, yet Joe fires seven times.