According to "Once Upon a Time in the Italian West" by Howard Hughes
, Sergio Leone
spotted a tree, while on location, that he thought would be perfect for the hanging tree at the beginning of the film, so the tree was dug up and relocated. See more
When the Rojo gang ambush the Mexican army unit the gun Ramon uses to kill all the troops is a Mitrailleuse volley gun. Each barrel had to be laboriously loaded by hand before all barrels were fired together in a single volley. However, the film shows the volley gun being used as a form of machine gun. The only machine gun around at the time was the hand-cranked Gatling gun which the soundtrack also seems to depict. See more
You see, I understand you men were just playin' around, but the mule, he just doesn't get it. Course, if you were to all apologize...
I don't think it's nice, you laughin'. You see, my mule don't like people laughing. He gets the crazy idea you're laughin' at him. Now if you apologize, like I know you're going to, I might convince him that you really didn't mean it.