Near the end of the movie they show a street scene that is supposed to be El Paso Texas but on the side of a building it advertises the Oklahoma Wigwam the newspaper from the book and movie Cimarron.
In the first flight with Arnold & Fierro, they observe the train approaching a causeway over a valley at speed. They return to Chupadero to report to Villa. The next day, they fly over the train again, which is a few feet past where they saw it before crossing the same valley.
Condition of the paint on the left side of the fuselage near the tail just before the flight training scene.
Whatever the dubious scientific accuracy that men hit with bullets from a Colt type revolver are sent flying several yards through the air (the executed prisoners scene), it is certainly true that Newton's 3rd Law Of Motion means that the same level of force to do that would be sent back though the gun and therefore to the man (Charles Bronson) holding it - that he'd be knocked back like that each time he fired - yet the recoils are nothing like that powerful.
Helicopter rotor wash visible in the trees during the Conejos cavalry charges.
Obvious ropes due to flying hay in the wall scene.
Lee Arnold is hit in the back, on his left shoulder blade, with the flat side of a rifle butt, yet he fell down as though knocked out and remained unconscious for the rest of the battle.
In the El Paso restaurant scene, a woman diner stares into camera as it tracks by her table.
When Lee Arnold (Robert Mitchum) wakes from unconsciousness in a pile of corpses, one 'dead man', with his mouth agape, blinks as a fly crawls across his face.
At about 30m in, when 'dead' bodies are being loaded into a cart one man moves his arm as he is laid in the cart.
High-tension power wires are visible near Conejos just after Arnold lights his cigar.
A machine gun nest ambushes charging Mexicans by cutting down the first three over a wall with a short burst, but as hordes more come over the wall, the machine gun doesn't fire even though the sounds of it firing continue. The gun obviously jammed but the footage was used anyhow with firing sounds dubbed into it.
Urbina's mouth says "Yes" at the end of the condolence scene, but there is no sound.
There is reference to a hanging and a bandit-like 'caper' at Conejos that are never seen. Presumably, these scenes were cut or not filmed.
SPOLER: The "boy" who takes Villa's watch calls him "my General", but Villa is a colonel.
The scores of prisoners are allowed a sporting chance to make a break for the wall and freedom one by one whilst being shot at with a revolver. As soon as it became apparent that the task was hopeless (they kept being shot) they would surely have decided to make a mass break for the wall all at once - figuring that the revolver would only get 6 or so of them before they could escape instead of killing all of them like before - or better all rush the man with the gun all at once.