Two Mules for Sister Sara (1970)

Factual error: When Clint Eastwood catches an Indian arrow in his left shoulder, he instructs Shirley MacLaine to prime the arrow shaft with gunpowder, which he then ignites as she forces the shaft all the way through his shoulder. Presumably, the burning gunpowder would cauterize the wound all the way through his body, or that's what the filmmakers asked the audience to believe. In reality, gunpowder is historically well-known for causing gangrene in open wounds. With a shoulder full of gunpowder cinders, Clint Eastwood should have died of gangrene and sepsis by the end of the movie.

Charles Austin Miller

Revealing mistake: After Clint has shot the 3 would-be rapists, he is rifling through the pockets of the dead men. As he checks the pockets of the first guy he shot the "dead" guy in the background is breathing.

The_Iceman

Revealing mistake: The rattlesnake Hogan kills in the mission's ruin is fake: Its frontal part moves unnaturally stiffly, and its tongue does not flicker. (00:16:40)

Daniel4646

Hogan: Sister if you wanna bless em you bless em dry.

Hogan: I don't mind killing em for ya, but I'll be damned if I'm gonna sweat over em.

Col. Beltran: This is better than killing each other, no?
Hogan: I only figured there was going to be one funeral... Catholic.
Col. Beltran: Oh? I didn't know you were Catholic.