Factual error: Near the end of the film Butch is complaining about the living conditions they have to endure - jungles, swamps, snakes, night work - and Sundance sarcastically retorts "Bitch, bitch, bitch!" In 1908 the term meant just what it literally means: "Female dog." It did not adopt its current meaning of "complain" until much later. At the time the film is set - outside the context of "female dog" - it was considered to be a serious obscenity, and it would not have been used to describe something as ordinary as someone moaning about his living conditions.
Factual error: In the beginning, Sundance is accused of cheating at cards and the man accusing Sundance doesn't know who he is. To prove it, Sundance shoots the holster off the man and then the gun from his hand, and then shoots the gun around the room. All this takes 9 bullets. The gun is a revolver holding 6 bullets.
Revealing mistake: In the opening sequence when Sundance shoots the gun belt off the card player, the film was cut to make the quick draw appear faster. You can see Butch's image jump across the screen in the background.
Continuity mistake: In the bicycle riding scene where Butch lets Etta ride on the handlebars, you can see her feet are resting on some sort of pegs protruding from the axle on each side of the bicycle wheel. When she is not riding, the pegs are not there.
Revealing mistake: In the scene where Strother Martin is leading Butch and Sundance back with the payroll Strother is shot dead. While he is on the ground Butch and Sundance scramble down near his body. You can see Strother's eye twitching from the kicked up dust.
Answer: It's to show how Butch and Etta care about each other as friends and that Etta is not just someone Butch has to put up with because she's Sundance's woman. A strong bond unites the three of them.
raywest