Revealing mistake: Jack Elam gets bothered by a fly crawling over his face (nice stunt, actually). When the fly moves over the bench, just before he catches it with the muzzle of his gun, look at the hind legs. You'll notice that the fly is dead. (00:07:50)
Revealing mistake: When Jill get's off the cart at the post station look how the light falls on the cart with the luggage and the rock in the background. It obviously comes from opposite directions. (00:31:05)
Revealing mistake: In the morning after Cheyenne's visit Jill attempts to leave Sweetwater for the second time. She carries a lot of luggage to the stable, and it's very obvious that it's all empty. (01:11:30)
Revealing mistake: When Jill offers herself to Cheyenne she puts down the kettle on the table so hard that the lid falls off. If you look closely (slow motion helps) you see the lid dangling by the knob between her fingers before she puts the kettle down. (01:03:10)
Answer: "Leone fools us into thinking that Harmonica is a criminal and sexual predator in the scene in Jill's barn in which Harmonica rips off the white lace beneath the bodice of Jill's dress. This act, that seems to betoken sexual aggression and to anticipate rape, is actually one of protection. Harmonica represents no more of a sexual threat than Cheyenne does. What Harmonica realises, and Jill does not, is that Frank's sharpshooters wait for her in the hills above her house and that the white of her dress makes her an easy target. He might have explained this situation more carefully to her, of course, but Leone's characters seem to almost thrive on, or to court, ill opinion. Moreover, when Harmonica's shots ring out at the well and Jill realises he is actually intent on protecting rather than brutalizing her, the effect is all the more dramatic for his having given her no hint of his intentions. Leone's heroes do not like to wear their morality on their sleeves." (John Fawell).