Revealing mistake: When they are learning how to throw knives, the guy gets one thrown through his hand. If you watch this carefully, blood starts coming out of his hand before the knife hits. (00:28:45)
Continuity mistake: As the Roger Young is breaking up, the ship's captain is running from the bridge and falls down with the large door descending and striking her midriff. As it hits, she spews blood from her mouth against the side of the door in a arching/sweeping motion. When Carmen returns to help free her, the blood is not displayed in the same pattern, more concentrated to one area as opposed to swept. (01:44:10)
Continuity mistake: In the scene where Rico is first in boot camp and Dizz says she is being transferred to the unit, she gets ready to fight the drill sergeant. She drops her papers, her jacket, and her bag. It cuts away for a few seconds, then goes back to the drill sergeant and Dizz in fighting stance. The piece of paper is farther back than before, this can be overlooked because of wind, perhaps. But the jacket and bag are both gone. (00:25:55)
Continuity mistake: Rico is running up the ramp to capture the red flag and drops his gun; it lands with the strap towards the top of the ramp. In the subsequent wide shot, the strap is towards the bottom of the ramp. (00:37:15)
Continuity mistake: In the scene where Rico is getting ready to go to the end of school party, he puts on his black jacket and for a brief moment, we can see the collar is turned up at the back. During the following conversation with his parents he never adjusts his collar, yet when he turns his back, the collar is neatly in place. (00:12:35)
Chosen answer: They do use nukes (to clear out bug caves) and fuel-air bombs (like they do before landing troops). It's possible biological and chemical weapons don't work on the bugs because of their physiology. Only nukes and Thermobaric weapons work.
lionhead