Continuity mistake: In Thessaly, as the two armies face each other, the large branches all over the center battle ground change or disappear entirely, depending on the angle of the shot (note the cliffs on one side and the trees on the other side). (00:02:40)
Continuity mistake: A boy is sent to get Achilles, to battle what he later says is, "The biggest man I've ever seen." In the shot facing Achilles, as the boy tries to wake him, Achilles firmly grabs hold of the boy's right arm. However in the next shot facing the boy, Achilles has him by the neck to pull him closer. (00:05:35)
Continuity mistake: When Achilles is burning Patroclus' body, the moonlight reflects slightly off his arms. While a body is burned, a person with a torch is always beside the one who places the coins, so the firelight would've shined off Achilles' arms as well, and yet it doesn't, indicating that the scene was not shot continuously.
Continuity mistake: After the Trojans were ordered to push forward after the Greek's first attack, blood can be seen suddenly appearing on a few of the Greeks shields.
Answer: They didn't know the Greeks weren't bringing cavalry. The Greeks did use them and sometimes brought them by sea. It was there to stop a cavalry charge and to break up fighting formations.
LorgSkyegon