Early in the film in the prison, several characters are shown in separate scenes carrying a lantern and appear to be dragging an electrical cord attached to one of their legs. Although there is a candle in the lantern, the light coming from the lantern is so constant and bright that it is obviously coming from an electric light bulb shining down from the top of the lantern.
Pedro constantly refers to the Inquisition as LA SANTA HERMANDAD=THE HOLY BROTHERHOOD, which any reader of DON QUIXOTE can tell you was actually a rural constabulary that was a predecessor of the Guardia Civil. The correct name of the Inquisition, which did not arrive in Mexico until after Cortes' death, is SANTO OFICIO DE LA INQUISICION=HOLY OFFICE OF THE INQUISITION.
Before their march at the end of the film, the priest addresses the crowd, saying, "The sun shines as fair here as in Spain." The sun was not shining brightly at all and the natural outdoor light was quite gray and subdued. As clearly seen, the reason for this is because the sky is filled with the smoke and steam from a massive erupting volcano.
When an announcement is made in the town square in Cuba, it is preceded and followed by an extra who makes a poor attempt at playing a roll on a conga, with one hand tripping over the other. As Cuba is the home of the conga, there were hundreds of local experts who could have played it properly and at three times the speed.