When Major Jackson prepares to kill Django in the bar, Maria is missing from the flight of stairs that are seen over his shoulder. She reappears just before Jackson leaves.
In the town shootout where Django assaults Jackson's Klansmen with his machine gun, many of the Klan members are shown being killed in multiple shots at different times (for example, a Klansman in a light gray buttoned-up jacket near the front of the gang is killed at least four times).
Early in the movie, Maria is tied and whipped by a group of Mexicans, the back of her dress is torn open the welts from the whip are visible. Shortly after the Red scarves kill the Mexicans and Django kills the Red scarves, he helps Maria get up. Her back is to the camera and there are now welts from the whipping a few minutes before.
When Django hides between the trunk, we can see a blue sign. However, in the following scenes it disappears.
In several scenes, Django's machine gun fires uninterrupted for minutes on end. A machine gun of that kind would most likely overheat in the time used to fire the weapon.
Promotional materials for Blue Underground's releases of the film proclaim that the Italian version uses Franco Nero's voice for the character of Django. This is incorrect--Nero was, in fact, dubbed by actor/voice actor Nando Gazzolo.
Rodriquez dumps what appears to be greater than a cubic foot of gold on the floor at his headquarters. He and Django carried it out of the Mexican fortress. That much gold would weigh at least one metric tonne. There is no way it could be held in a canvas bag and carried by two men. It's far too heavy.
One man could not possibly operate a Gatling gun without it being mounted on a tripod or a carriage. The weight of the gun (~150 lbs) normally takes a four man crew. That's not even considering the recoil. Gatling guns fired 400 rounds per minute by the 1880s. But even at one round per second (post Civil War) - 60 rounds per minute - the recoil would be far beyond what one man could handle, without the gun being mounted on a tripod or a carriage.
Whenever the belt-fed machine gun fires, the belt doesn't move at all.
Modern suburbs can be seen in the distance behind Brother Jonathan in his close-up when he creeps in from the alley.
The belt feeding the cartridges into Django's machine gun is far too short for the number of rounds being fired in any of the scenes it is used in, and the belt isn't being fed through the firing mechanism.
The muddy town streets have tracks from large rubber tires.
The bartender Nathaniel accompanies the piano-player on the fiddle, but his violin has no bridge; the strings run off the end of the fingerboard and directly to the tailpiece. The most any player could get out of such an arrangement would be a couple of high-pitched squeaks.
According to the subtitles of Blue Underground's DVD release, General Hugo describes Maria as being "half Incan and half Mexican", despite his actual dialogue indicating that she is "half Yankee". This was corrected for the Blu-ray's subtitles.
As Django goes stealing the gold, the chatter track from the Mexican party repeats itself multiple times. For example, a Mexican can be heard saying something to or about "Natanièl", much to the amusement of the others.
With the exception of a sawed-off shotgun used by one of Jackson's men, the firearms shown throughout the film are historically inaccurate for a film set in the years immediately following the American Civil War. These weapons are the Colt Single Action Army (first made in 1873) and Colt New Service (1898) revolvers, Django's machine gun (a fictional model with a barrel based on the 1866-71 Montigny mitrailleuse, but a firing mechanism and belt-fed magazine inspired by the 1895 Maxim gun), and the Winchester 1892, 1894 and 1906 lever-action rifles.
When Django tells Hugo that Maria "is not his type" in the Italian version, his lips don't move. This does not apply to the English version, were Django says nothing at this point.
When Django pulls out his coffin to show Hugo and his men in the Italian version, Hugo's jaw can be seen moving, but no words come out. This is not present in the English dub, where Hugo is heard saying, "What the hell is it?"
When Django discusses his machine gun and plans to take Major Jackson's gold, a considerable amount of background chatter is heard. However, few, if any, of the bar patrons are actually engaged in conversation--they are instead watching Django and Hugo's own conversation.
On the Blu-ray release by Blue Underground, Django's line "Let's go, Maria" is removed from the English version, resulting in Django's lips moving without him saying anything.
After Django kills four of Jackson's men in the bar and twirls his revolver's trigger guard on his finger, he (uncharacteristically for a highly skilled gunfighter) fumbles while trying to pull back the hammer when aiming the revolver at Jackson himself.
After Django smacks Ricardo with the butt of his own rifle and throws it back to him, Ricardo angrily readies the rifle with the intention of shooting Django. Although a metallic clicking sound is heard, he is actually shown to be miming the action (presumably by mistake)--his hand is not within the lever.