Factual error: Captain Barbossa's ship has a modern Union Jack flying on the stern. The film is set in the reign of George II (1727 - 1760). The flag shown includes the cross of St Patrick, although Ireland did not become part of the United Kingdom until 1801, and the Union Jack at the time of the film would have comprised only the crosses of St George (England) and St Andrew (Scotland).
Factual error: The soldiers chasing Sparrow in London have red cockades on their hats. They should be wearing Hanoverian black cockades, as George II was the second king of the House of Hanover.
Factual error: After the mermaids scene, when Blackbeard, Jack, and the others start walking through the next island to find the silver chalices, two distinct bird calls can be heard. Both are native to Australia - they are the Magpie Lark, also known as the Peewee, and the other is the Willie Wagtail. Both birds are not found anywhere remotely near the Caribbean.