Revealing mistake: When Herod shoots Rusty in the back before the final gunfight, a car can be seen driving down the road in the background.
Revealing mistake: In the scene at the end of the movie where Lee Marvin is running interference during the escape by shooting in the air, horses pulling a beer wagon get startled and run into the street where the wagon turns over. At the beginning of the shot, when the horses begin to bolt, you can see the stuntman driving the wagon. He is sitting low behind the wooden front of the wagon (which has holes cut in it so he can see out).
Revealing mistake: When The Deputy Charley Rakes goes to Cricket's house and attacks Jack, you see Charley throw Jack down the steps outside the house. If you look closely, you can see he lands on something really soft and spongy like a mattress which is hidden under the foliage on the ground to break his fall. When Charley walks down the steps towards Jack, you see him walk on it, which again looks really soft and spongy.
Revealing mistake: The caboose and two bunk cars are uncoupled and sent rolling down the hill, with troops locked inside. As the cars roll off a cliff, troops can be heard yelling. However, as the cars hit the ground and shatter into rubble, the wood does not appear to be blood stained, nor does there appear to be any sign of bodies in the debris. The cars were obviously empty for the scene, and given the circumstances of the soldiers allegedly trapped within them, it's unlikely that any of the soldiers could've gotten out in time.
Revealing mistake: When we see a wagon with a woman and several children in it, the horses get spooked and run. A woman is seen desperately trying to stop the runaway horses. In the next scene you can see the children are not real and the woman is a man dressed in a woman's dress, obviously a stunt man used for that scene.
Revealing mistake: After the trailer explodes on the bridge, towards the end the truck swerves to the left. As it drives off the bridge there is no tail shaft between the gearbox and front diff - the truck falling off the bridge is just a shell.
Revealing mistake: In the Gatling Gun scene when the camera cuts to a short couple frame shot showing a closeup on the .45-70 Government ammunition casings on the ground that are falling from the gun, the casings are star crimped. Star crimped casings indicate blank ammunition. Standard ammunition isn't possible with star crimping. The size and casing shape indicates .45-70 Gov which was popular in these guns at this time. (01:46:40)
Revealing mistake: In the scene where the boy is shot in the leg and the carried away by an unionist soldier you can see more union soldiers storm past them. The bayonets of the soldiers are obviously made of rubber as they are dangling while the rifles are moved up and down by the running soldiers.
Revealing mistake: The outline of Divine's wig is obvious during the closeup when she's scolding her donkey at the beginning.
Revealing mistake: When Caleb shows Mae his horse and it rears you can see the man holding the horse's rope is not Caleb. The man has an older, redder face and greyed sideburns. (00:08:21)
Revealing mistake: When the protagonist jumps two of the evil cowboys that are after his jewels, the stuntman on the right tosses aside the rifle in a quick deliberate move pretending to lose it. (00:10:25)
Revealing mistake: When Bud and Wes take competitive turns riding the bull at the presumed high speeds, the bucking patterns and timing aren't consistent. A few times either man goes less than 15 seconds on a mid speed rather than full on bucking. Which even for a practice doesn't add up, and wouldn't fly during a competition.
Revealing mistake: In the scene when Crow Horse and Levoi are running from Coutelle and the "GOONS", they go off-road toward the stronghold. You can see in the grass the tire tracks from all the other takes. Especially as there is no reason any vehicle would leave the road at that place otherwise.
Revealing mistake: Near the end of the movie, the Bunch are relaxing and passing around a bottle of whiskey. While the actors could not be expected to drink real alcohol, it's too bad the prop guy could not have mixed up some less foamy instant tea, typically used as a substitute in these scenes.
Revealing mistake: In each one of his scenes, every time you see Captain Fuller you can see that the actor is wearing contacts to make his eyes blue. It's obvious contacts with the brown rings of his natural eyes around them. And contacts were not invented for a long long time after this movie takes place.
Revealing mistake: When Potter starts shaving at the morning of the Indian attack on the wagon train, his mirror falls off the post, and as he bends down to retrieve it, an arrow embeds itself right above his head. If you look closely in that scene, you can see a length of targeting wire used to guide the arrow sticking to the post above Potter's head. (00:37:10)
Revealing mistake: The Giles brother who got "hung" when he fell after getting shot by MacMasters can be seen moving his body (mostly arms). (00:04:06)
Revealing mistake: At the end after the driver of the wagon has fallen off and the horses are running wild you can see a slot in the front of the seat and arms holding the reins.
Revealing mistake: Stan is using a block and tackle to hoist Ollie up to the balcony of Finn's apartment. When Stan lets go of the rope, Ollie falls and lands flat on his back. It is obvious by the awkward angle of the legs that a dummy was used. In addition, the dummy lands with the legs close together but in the shot that follows, Ollie's legs are far apart and one leg is in the air.
Revealing mistake: Many of the cavalry soldiers were carrying M-1 Garand rifles (WW2 era rifles).