You can see a car passing by in the background when Tuco is balancing on the cross on the graveyard in the end of the movie.
After setting the explosives under the bridge, Tuco and Blondie jump into a foxhole and are perfectly dry, despite having been soaking wet from the river just previously.
When Tuco and Blondie are under the bridge in waist-deep water strapping dynamite to the supports, a car passes from right to left where the poles form a V to the right of Blondie's hat just after Tuco says "You go first."(widescreen edition)
The American flags flown by the Union army have 50 stars, 97 years too late for the film's setting.
When Tuco and Blondie are carrying the crate with the explosives on the stretcher, it has turned about 90 degrees between the two shots when the music starts playing.
When Tuco and Blondie seek Angel Eyes in the deserted town, they discover a note that says "see you later idiots" but if you look closely at the paper, it is actually a page of the film script.
When Tuco and Blondie ride their coach up to the mission to recuperate from the desert several power poles are visible in the background to the left. (May only be visible in the wide-screen version). However, one can make the assumption that these are telegraph lines since the telegraph was a common form of long-distance communication during the civil war. Power poles are even visible by the train tracks when Tuco escapes his captive which makes sense since telegraph lines were commonly built along railroads.
When Wallace is escorting Tuco on the train to their destination, presumably another prisoner of war camp, Tuco pushes him off the train and after rendering him unconscious, tries to sever the chain joining the handcuffs on both of them. But Wallace would have held the keys of the handcuffs, so why didn't Tuco search his pockets, as a first measure. After Tuco manages to sever the chain on the rails, he would still have had his part of the hand cuffs on his wrist, but shortly after, we see Tuco in the bath and no cuffs are to be seen.
When Tuco is balancing himself on the cross at the end of the movie, a motor vehicle is visible on the right. It is moving right to left.
Blondie and Tuco walk down the street of the desert town to confront the Angel Eyes' gang. At the beginning, their shadows are projected to behind them. Next shot, the shadows are projected in front of them.
Blondie lights a cannon to fire at Tuco but the cannon is facing the graveyard, the opposite direction to where the battle has just taken place across the river.
At the end of the movie Blondie flips up the long-range leaf sight on his rifle but the cross member is so loose it falls down to the very bottom. This would give him no elevation of the gun barrel to allow for bullet drop, at the 1000 yards he must have been at, to make that shot.
During the final show-down by Tuco, Blondie and Angel Eyes at the cemetery, Tuco has no bullets in his gun but you can see a flash from his pistol when Blondie shoots Angel Eyes. However, this is the sun glittering on the barrel of his gun, not a muzzle flash.
Blondie drops Tuco off in the desert and then turns around to go back to the same town he just came from where the sheriff and his men have just witnessed his scam of saving Tuco.
During the three way showdown, Tuco slowly pulls his pistol out from his pocket and dangles it beside him, which unknown to him Blondie has emptied. But a professional gunman like Tuco is supposed to be, would easily be able to tell the difference in weight between a loaded gun and an empty one.
During the preparation of the charges on the bridge supports, they are connected in series, and Blondie lights only one (too short) fuse. When the bridge blows, all four charges detonate simultaneously, since they were detonated electrically.
When Blondie is comforting the dying Confederate soldier near the end of the film, he gives him two puffs of his cheroot cigar - it changes length by almost an inch from shot to shot, first longer, then shorter, then longer again.
When Blondie kicks the lid off of Arch Stanton's grave, the lid slides sideways along the ground. But, in the next shot, the lid almost hits Tuco in the face, like it was kicked upward.
Near the end of the film, when Tuco's head is in the noose in the cemetery, the tightness of the knot keeps changing between front and rear shots.
After Angel Eyes is shot the second time, his gun falls at the front side of open grave towards the central area. When Blondie shoots the hat, the gun appears at right side of the grave.
In the final scene when Tuco is shot down by Blondie, the position of the rope changes while hanging around Tuco's neck. First it is hanging vertically in front when he steps into the courtyard. Then it is slung over his left shoulder in the close-up.
Blondie shoots Angel Eyes' hat into the grave and it lands on his chest. In the next shot, the hat is in a completely different position.
Tuco is wearing a Confederate uniform after he kills Wallace but is later seen in town wearing different clothes with no handcuffs around his wrists even though he only broke the chain.
Blondie goes from town to town handing Tuco over to the authorities and then saving him without ever wearing any form of disguise. Yet he never becomes a wanted man himself.
The Commendant of the Union prisoner of war camp is referred to as "Captain" but he wears the shoulder-straps of a Union Major.
When the Sheriff unrolls the wanted poster in Tuco's face the poster clearly has a photograph of very good quality instead of a sketch which seems highly unlikely at the time the film takes place.
When the POW camp commandant is upbraiding Angel Eyes for his treatment of the Confederate prisoners, Angel Eyes responds with a comment about the treatment of Union POWs at Andersonville. Andersonville was opened in 1864. The Film is set in 1862.
Note that in all the desert scenes, there are no cacti visible. Cacti are found only in North and South America, making it obvious that this was filmed in the Old World; in this case, Spain.
When the rhythmic music stops and Tuco is choking after screaming "Blondie", a person walking to the left can be seen on the left side of Tuco's face. You can also see a sun reflection on something carried by the person.
The bounty hunters that Blondie saves Tuco from at the beginning are waiting for Tuco to come riding towards them. Tuco hasn't being stationary, and he isn't being pursued to set him into a trap, so there's no way the bounty hunters could have possibly tracked him and predicted where he was going to be.
When the runaway Confederate carriage first appears in the desert you can see someone steering it. Then, as Tuco seizes the horse-team to stop the carriage, the reins are obviously being held by the out-of-frame driver. In the next shot, viewed from the driver's bench, the reins visibly tighten to halt the horses and then drop.
All of the railroad cars seen are four-wheeled. This design had fallen out of favor in the United States by the 1850s.
In the store scene with Tuco, he and the owner pass by several crates of black powder marked "ACME." ACME was a generic name for companies that came into use in the 1920s to enable them to appear on the first page of most phone books. It would not have been in use in 1862.
Tuco examines a Belgian 10.4mm Galand revolver in the gun shop. This gun was not invented until 1867.
When Angel Eyes first enters Stevens' house, an electrical tower can be seen in the background over his left shoulder.
If each gold coin had approximately 1 troy ounce of gold in it worth $20, $200,000 implies there were approximately 10,000 coins in the eight bags that Blondie and Tuco recovered. The weight of those 10,000 coins would be (10,000 coins * 1 oz/coin * 31.1 g/oz * 1 kg/1,000 g * 2.2 lbs/kg) = 684.2 lbs. Each bag would then weigh approximately 85.5 lbs. Blondie is seen loading up his horse with the gold two bags at a time (170 lbs). It doesn't seem likely that a person could lift that much gold without much more difficulty.
When Blondie is lifting the heavy bags of gold to load them on his horse, you can see a parked car on the far left.
Angel Eyes' grip on his spoon changes from overhand to underhand back to overhand while he chats with the rat.
Tuco has Blondie put his head through a noose and the way the rope is looped around the roof beam changes after the cannonball strike.
When Tuco is walking down the street to confront Angel Eyes men, he suddenly turns and pulls his pistol on Blondie. You can clearly see that the gun is unloaded (i.e, there are no cartridges in the cylinder).
As Blondie and Tuco are setting the explosives to blow up the bridge, they are in sight of both the Union and Confederate positions. Neither side wants the bridge destroyed according to the Union Captain, yet neither side shoots at them to prevent them from setting the charges. However, given that Blondie and Tuco carried a stretcher to the bridge, both sides would have most likely assumed that both were medical corpsmen checking on the dead soldiers in the river, and would not have expected them to plant explosives on the bridge and blow it up.
In the prison camp scene where the musicians are playing while Tuco is being beaten by Angel Eyes, the fiddle has fine tuning adjusters on the tail-piece. These fine tune adjusters were designed for metal strings used many decades later.
During the bridge scene with the explosives, the fuse is often seen in the water. Would this mean it could not burn? No, because fuses were coated in wax, lots of mine & tunnel work back then occurred in damp & wet conditions.
When Tuco prepares a bath that's been deserted, he pours bath salts into a tub already full of water. When the bounty hunter enters, Tuco is in the bathtub covered in bubbles. Pouring bath salts into an already filled tub doesn't create bubbles, especially when the water is cold.
When the two armies battle at the bridge, the Confederates are using the flag with the blue criss-cross on the red field. This is not the Confederate national flag, rather it is the banner of Gen. Robert E. Lee's Army of Northern Virginia. It would have been in battles in the east, not in the west.
When Tuco (Ugly) runs up to the carriage filled with dead bodies, he opens the gate to the carriage and looks in. It can clearly be seen that the guy lying to the left is clearly blinking, even though everybody in the carriage except Bill Carson is supposed to be dead.
The man pointed at as the Confederate General Sibley (by the hotel owner) is actually a Confederate Captain according to the rank insignia on his collar. The buttons on his uniform is furthermore misplaced compared to that of a authentic Confederation Captain. A genuine uniforms buttons would have been closer to the chest.
When the POW's march into camp, they cause the short bridge to bounce violently. Marching troops should always be ordered to stop marching when on a bridge because the rhythmic vibrations can cause resonance that can potentially damage, or even lead to the complete collapse of the structure. This is why the bridge into the camp bounces so dramatically.
At the Union prison camp, Tuco sees Angel Eyes and tells Blondie, who responds "Yeah". But Blondie hasn't met Angel Eyes prior to this moment. Even if Blondie knew Angel Eyes before the events shown in the movie, as Tuco did, Tuco couldn't have possibly known that Blondie had met him before.
In one scene, Tuco praises Lee and damns Grant out loud to the troops coming out of the desert. However, the movie takes place during Confederate invasion of New Mexico Territory in February- March of 1862, when both Lee and Grant were unknowns at this time. Lee didn't assume command of the Army of Northern Virginia until June 1862. Grant was a relative unknown when he won his first victory at Fort Donelson in February, 1862, hardly enough time for Tuco and Blondie to know who he was. That being said, in another scene, Angel Eyes mentions Confederate abuses in Andersonville Prison, which only became a prison and started accepting prisoners in February 1864.
Blondie is seen shooting Tuco's rope with a Sharps 1874, 12 years too late for the film's setting.
The dummy used for Corporal Wallace as he is dragged under the train, doesn't match his size in width and height.
The battle-scenes show at least two Gatling guns, forerunner to the machine gun. The Gatling gun was patented in Feb 1862 but did not see action until mid-1864 while the movie takes place early 1862. The Gatling gun first saw action in Virginia during the Petersburg siege of June 1864. The Gatling gun was not formally introduced into the U.S Army until 1866.
Angel Eyes offers Tuco some of Bill Carson's tobacco. When Tuco reaches into the tobacco holder to help himself, Angel Eyes slams the lid shut on Tuco's fingers. However, you can hear the lid snap shut despite Tuco's fingers being pinched (and therefore preventing the lid from snapping shut).
The second hat shot off by Blondie also briefly separates the actor's toupee from his head. However, it's quite plausible for a man to have worn a toupee in 1862.
Angel Eyes uses a 1858 New Army Model Remington revolver, a cap-and-ball revolver commonly used during the Civil War. However, he wears a cartridge belt with metallic cartridges that do not fit his weapon.
A man in Tuco's profession should have realized before engaging in the final three-way showdown that his revolver would not have fired. It is clearly visible that the percussion caps on his revolver have been removed. In contrast, such percussion caps are clearly visible on the cylinder of Angel Eyes' pistol.
Blondie's rifle is a 1866 Winchester 'Yellow Boy'. Although the production team removed the wood fore stock to disguise it as an 1860 Henry (which was available during the Civil War), the biggest giveaways are the loading gate on the right side, the lack of a magazine tube loading break switch, and the lack of slits in the magazine tube which allows the user to see how many bullets are left in the gun.
Tuco and Blondie blow the bridge using what appears to be dynamite, first used after the war ended. If you examine carefully, they appear to be gunpowder charges wrapped in paper.
When Blondie says, "Your spurs," and shoots the last of the three ambushers in the hotel, the man falls backwards, knocking the wall and making it wobble.
The character "Jackson/Bill Carson" is referred to as a member of the 3rd Regiment in the Confederate Army. During the New Mexico campaign the Confederates deployed the 2nd, 4th, 5th, and 7th Regiments of the Texas Mounted Rifles and some unnumbered territorial groups. There was no Confederate 3rd regiment of any sort, although the 3rd U.S. Cavalry did participate on the Union side.
In the cemetery scene when Tuco is balancing himself on the cross, you can see a person standing in the background, just to the left of his head.
Before Blondie enters the water for the first time his coat is already wet. He was walking through a puddle before, but it could not have produced this amount of wetness.
In the opening, when Eli Wallach is shown in close-up, he has an obvious cap or crown on a tooth.
In the retreat scene in the town a large unit of Confederate foot infantry is shown as marching with the retreating column. In reality, Sibley's force consisted entirely of mounted units and a single battalion of artillery. No foot infantry were used in the campaign on the Confederate side.
At the graveyard Tuco runs around quickly glancing at all the graves until he spots Arche Stanton (partially covered though readable). Earlier he shows that he cannot actually read, Blondie has to read "idiot" from Angel Eyes' note on the dead body.
When Blondie and Tuco are carrying the explosives on the stretcher, at first the stretcher is missing several wooden slats, but as they approach the bridge, it changes into a completely different stretcher with no missing slats.
Leading up to the final gunfight, there are several close ups of Angel Eyes' hand creeping toward his gun. The gun is clearly a Remington percussion type, but there are cartridges visible on his gun belt.
One of the three bounty hunters that shoots Tuco's horse has a piece of grass in his mouth just prior to been shot by Blondie, that was not there in the previous frames when he tells Tuco he has a face worth 2000 dollars.
After Blondie tells Angel Eyes of six being a perfect number because it is the number of bullets his revolver can carry, the latter gives off a laugh that audibly belongs to neither Lee Van Cleef nor Simon Prescott (Van Cleef's voice-over actor in the extended version of the film). The laugh belongs to Angel Eye's voice actor in the Italian version, Emilio Cigoli, so the presence of his laugh in the English version is a dubbing error in the extended English-language version.
Before the final gunfight, as Tuco is standing in the circle, he lowers his hand to the level of his pistol. His hand was already there in a previous shot.
When Tuco is balancing on the cross at the end, the knot of the noose is above his head when shown from the front but it is close to his neck when shown from the back.
When Angel Eyes enters the house at the beginning you can see a radiant station antenna in the background.
At the start, when Angel Eyes is first seen, the boy stops the burro and the well's cross beam is in front of, and slightly above his head. In the next shot of the boy, the burro hasn't moved but the cross beam is now behind his head.
The date of death on Arch Stanton's grave is 3 February 1862 - a few months before the setting of the film. The body inside, however, has undergone several years of decomposition.
The Union force at the bridge is of considerable size. Three companies announce their readiness, suggesting a battalion at least, and there are also numerous guns. Yet the entire force is under the command of a captain. In reality, the senior officer would most likely be a brigadier general.
When Angel Eyes throws the shovel at Tuco by Arch Stanton's grave, he nearly hits Tuco in the head.
Angel Eyes is seen smoking a pipe, which is clearly a Peterson 'System' pipe. Peterson was founded on Grafton Street, in Dublin, Ireland by Friedrich and Heinrich Kapp in 1865, and joined by Charles Peterson, who was responsible for the design of its premier product, the Peterson 'System' pipe. It was introduced in 1890 and further improved with the invention of the 'Lip' mouthpiece in 1898.
Tuco is seen inspecting a Galand Revolver, invented in 1868.
At the POW camp, Angel Eyes' henchman, Wallace, gives Tuco the mother of all beatings. Tuco would have been in no shape to get up, never mind walk, yet next day, Tuco is walking in the train station with Wallace and there is not a visual mark on him.
During Tuco's beating in the POW camp, one of the fiddlers stops playing. The singers behind him are still singing but only the music is heard.
The POW band guitarist is shown strumming his instrument, but the soundtrack guitar is "finger-picking." There are other mis-matches in the scene, including actors playing valve trombones which aren't heard.
Right after the scene where Blondie places the rock in the middle of the courtyard, (presumably containing the name of the grave), there is a close-up shot of Angel Eyes' face lasting about one second. To the right of Angel Eyes' head, you can see a person running in the far background. They are moving right to left.
Blondie and Tuco are seen using dynamite to destroy a bridge,however dynamite wasn't invented until 1867,5 years after the movie was set.
Before blowing up the bridge, when Tuco tells Blondie that the money is on the other side of the river, he is loading metallic cartridges in an (historically incorrect) modified Colt Navy. However during the final three-way showdown, his Colt Navy is a true 1851 model with nipples for percussion caps.
Blondie is shown cleaning his (historically incorrect) revolver by simply running a brush through the barrel and the cylinder chambers, from which comes out a small puff or dry dust. In reality, black powder (the only gun powder available at the time of the Civil War and for the following thirty years) after a relatively short use produced a thick, grimy, smelly, CORROSIVE fouling that tended to jam the gun's action (to the point that sometime it was necessary to turn the cylinder by hand!) and that had to be painstakingly cleaned (soap and hot water was the best way) to keep the gun working and to prevent irreversible corrosion.
When Tuco is apprehended in the beginning by Blondie and the Sheriff compares the wanted poster to Tuco's face to make sure he is the right man, the picture shown is of incredible quality, much higher grade then what was probably available for 1862 technology.
Tuco is ambushed by three bounty hunters with one of them firing an anachronistic Winchester rifle at Tuco to make him fall off his horse. The bounty hunter with the rifle is heard working the loading mechanism yet when he enters the frame he is seen pulling the hammer on the rifle. If he had really used the loading lever of the rifle the hammer would have already been pulled down.
When Tuco enters the gun shop, he hangs the "CLOSED" sign at a downward-right angle on a nail on the back of the front door. As he exits the shop, the "CLOSED" sign is angled slightly down to the left.
At the prison camp Tuco recognizes Angel Eyes among the Union soldiers. And later, during the interrogation, Angel Eyes calls Tuco an old friend. Yet they have never met in the film, nor is any relationship between them discussed among the characters.
When Tuco is shooting at Blondie's canteen in the desert, the sound of the shots does not match the impact of the bullets.