The chain tying El and Carolina together is removed with an electric wire feed welder (used for welding) and not a blowtorch (used for cutting), removing the links closest to the cuffs. When it falls to the ground, it is whole again.
Before the guitar maker presents his work to El Mariachi, he is shown playing it left-handed. In the next shot, he is strumming right-handed. Then, as he hands it over to El, it is positioned as if he had just been playing left-handed again.
In the opening scene, after Belini leaves the bar, Sands is seen taking off his fake arm with the yellowish piece of paper on the table in front of him containing the information given to him by Belini. The shot then shows Sands putting his fake arm in the bag, and when the next shot cuts back, the paper is missing from the table.
When Jorge uses white out to cover the INVALID stamp on his
FBI badge, it is a sloppy job that will pass only the most casual inspection. Later, when he flashes the badge to Billy it looks perfect with no indication of alteration. However if you look carefully you can see the white "INVALID" writing on the badge. When Ajedrez subsequently has the badge, the white out is once again very visible.
When Lorenzo is practicing shooting, he takes his brother's bottle of alcohol and places it on the wall to shoot. The drunk picks the bottle up, and while he holds it, Lorenzo shoots it. They cut away to show Lorenzo, and when they cut back to the brother holding the bottle, the bottle has broken differently, and had a label.
El, Lorenzo, and Frideo are standing outside the church before going to preform for the president, El has a white ribbon tied in his hair, but when he walks into the church it's gone. A few moments later when the are on the roof his hair is up, then cut to Lorenzo and then back to El and his hair is down.
When Fideo arms the mobile bomb in the guitar case, he closes the lid. The next shot shows the lid still open as he stands up and sends the bomb on its way. The next shot shows the bomb with the lid closed as it moves towards its target.
When El shoots out the general's legs, you can clearly hear two shots, meaning his gun should be empty as it is a double barrel. However, he then walks up to the general and shoots him in the head without reloading.