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.
During the bicycle sequence at Butch's house, the front wheel alternatively goes between having pegs for Etta to stand on, to not being there.
When Butch and Sundance are being chased by the posse, scratches on their faces appear and disappear.
The amount of straw that hits Butch while he is riding the bicycle varies.
Chased by the special posse, Butch and Sundance split off from the other two outlaws in the middle of a field. After climbing a hillside Butch asks, "How many are following us?" and Sundance, looking back, immediately answers, "All of them," even though the posse has not yet reached to point in the field where the two trails diverged.
At the climactic shootout, the shoulder insignia of the Bolivian army officers are wrong. Instead of stripes, the shoulder boards should have six-pointed stars.
When Butch and the Kid are floating down the rapids, the stunt double for the Kid does not have a mustache.
During the climactic gun battle, Sundance fires his two six-guns at least 16 times without reloading. Obviously the guns would have to be reloaded after only 12 shots.
Obvious stunt double at the end of the bicycle riding sequence, when Butch is riding backward and crashes through the fence.
When Sundance jumps onto the train near the beginning of the film, and makes his way towards the locomotive, it is obvious that a stunt double jumps into the coal car and Robert Redford emerges - not enough time elapses from the point at which the double disappears behind the coal until the point that Redford rises up from the coal at a different position.
When they're eating at Etta's house, before and after Butch shouts, "You probably inherited every penny you got!" you can see Butch's shadow on the set.
When Butch and Sundance are being chased by the posse, and ride into the desert, they stop to look back. In the distance are some white buildings; look above them to the right and you'll see a modern vehicle, possibly a white box van drive along a road from right to left.
The saloon has electric light fixtures on the wall.
Percy Garris uses the phrase "Bingo" to emphasize a point. This expression didn't exist until the 1930s.
After their first Bolivian bank robbery, Butch and Sundance ride out of town at speed and up a slope. To the right of the shot is a very imposing stone building, down in the valley below; if you look below it and to the right you can see a light blue vehicle drive along, take a left turn, and reappear among the trees.
The locomotives on the trains are class K-28s, which were not produced until 1923, for exclusive use by the Denver and Rio Grande Western Railroad on their narrow gauge track in Colorado and New Mexico.
In the river, Butch says to Sundance, "You're drowning me! You're drowning me!" although they're apart at this point.
When the engine of the special train blows its whistle to signal the posse, the sound is that of a single-note whistle. But the close-up zoom shows that it is a six-chime whistle, which would make a radically different, lower-pitched sound.
All the Bolivian people have Mexican accents.
In the final shootout in San Vicente, there are trees all around the town and one in the plaza. The real San Vicente, Bolivia is at 4800 meters altitude (over 15,000 ft.), so is well above the tree line.
When Butch and Sundance are riding down the mountain with Percy to pick up the payroll, power lines and poles can be seen in the background.
After arriving in Bolivia, Sundance claims that he was born in New Jersey. In fact he was born in Pennsylvania.