Corrected entry: We see three immortals getting spears thrown at them. Watch the man in the middle. If you play frame by frame you can see the spear hit him in the mouth, bend and bounce off. (01:26:40)
Corrected entry: This movie takes place in 480BC. After the first attack on Xerxes' army, Xerxes talks to his aide. Xerxes says that his men are cowards. The aide says that his army can defeat any normal army but "the Spartans fight like machines." What machines existed in 480BC? (01:40:00)
Correction: There were plenty of 'machines'. The Greek theater employed what was called the "Deux ex machina" or 'god of the machine'. This was a dramatic contrivance by which a Greek god, goddess or Olympic emissary was lowered to the stage by a 'machine' consisting of pulleys and levers at the end of the story to set right all of the conflicts. Machines were also used to dig quarries and build the temples. Sorry, but this one is a little too picayune.
Correction: If you must go frame-by-frame to see this, it is not valid as a movie mistake.
Twotall