Other mistake: When the slaves are getting into the Portuguese ship (the "Tecora"), the crew shouts in clear Spanish (some Spaniard and some Mexican accent) rather than the expected Portuguese. (01:18:10)
Visible crew/equipment: When Brad Pitt is taken prisoner by the English, he tries to escape and is thrown in prison. As the camera turns back to the door, the shadow of a microphone is visible left to the door.
Factual error: Secretary of State John Hay is depicted issuing the order to "initiate hostilities" against Spain. Unfortunately, at the time we actually went to war with Spain, John Hay was not the Secretary of State. That position was held by William. R. Day. Hay did not become SofS until September of 1898, after most hostilities had ended.
Continuity mistake: When Hemeda is getting dressed in the presence of Nour El Sherif, he changes from being in his underwear to fully dressed in a complicated costume in a few seconds.