Factual error: Rescuer and US Marine Jason Thomas is an African-American in real life, but was portrayed in the film as a white man. The film's producers realized the mistake only after production began, and apologized to Thomas, whose identity had not been widely known for years after September 11th.
Factual error: Louis Simo gives his son an Etch-A-Sketch while taking him to school, and later when Louis stops by to see his son at his ex-wife's house, his son is playing with the Etch-A-Sketch in his bedroom. Both incidents take place in the summer of 1959. George Reeves died June 16, 1959, hence the investigation. The first Etch-A-Sketch toys were produced on July 12, 1960 and Ohio Art launched the toy in the United States in time for the 1960 holiday season.
Continuity mistake: When Leonidas, and presumably all the other Spartans, use their spears to clear their shields of arrows after the arrow shower from Persian archers, the tips of the arrows are still visibly left on all their shields. In the next shot, when the Spartans regroup for the Persian cavalry charge, the arrow tips are gone. (Granted, this is a highly stylized movie based on a comic book, but that does not change the fact that this is a continuity error.)
Deliberate mistake: In the scene where Marie is trying on shoes, a pair of powder blue high top Converse sneakers can be seen next to her feet. It must have been done intentionally, but since there is no trace of modern apparel anywhere else in the film (the closest would be the mere mention of hot pink dress fabric but, as it's not shown, we don't know what exactly Marie calls "hot pink") these shoes (and the fabric) can't be considered part of a thematic element or artistic license. (00:55:35)
Continuity mistake: At the end, during the fight scenes in the first class cabin, the number of overhead compartment doors that are open changes.
Factual error: When the Marines strip off and run into the sea in the final scene, Doc takes off a pair of white socks that would be more appropriate for a final at Wimbledon. Not only are they white rather than khaki, they are virtually spotlessly clean which would be impossible after a week of fighting on the black sands of Iwo Jima.
Continuity mistake: When Paul (the hotel manager) finds Timmons in the kitchen when Timmons had been shot and is bleeding, we see Timmons with his hands on his blood that is on his shirt. When Paul comforts him, he puts his bloody hands on Paul's white shirt, but when we see Paul outside the hotel, there is no stain from Timmon's blood.
Plot hole: When the Black & Tans are shown driving through the village, a blue house is visible behind them. The house has modern PVC windows.
Continuity mistake: When the Prime Minister is preparing to make his golf swing, his shawl is alternately bunched up and then spread out smoothly.
Factual error: Sharpe follows a wagonload of powder kegs into the Western Gatehouse, then down a corridor lit with torches, to the end of the corridor where Indians were tying together quickmatch, once again by torchlight. With the propensity for powder kegs to leak, even an Indian subadar would use closed lanterns.