Revealing mistake: When the guard that wants to kill the fool is hit by an arrow, you can see the outline of a protection plate or something like that under his clothes.
Revealing mistake: At the beginning of the film when Nester and Opelka and at least two other Americans are attempting to run towards the chopper, you hear a series of Vietnamese mortars which hit two of the Americans, followed by screams. If you look real closely at the last mortar to hit the second American, it is a scare-crow type figure dressed in military fatigues that takes the mortar hit.