Shortly after the perspective shifts to the Japanese side, the camera zooms in on an ammunition box. The casings around it are blanks that have crimped ends with no projectile.
As the platoon is getting ready to attack the cave, The lieutenant puts his binoculars down on a large boulder and checks his sidearm. A hollow thump can be heard as he puts the binoculars down on the hollow, fake boulder.
When Lt. Katell feed's a round in his pistol he puts it back in his holster with out putting the hammer on safe or put his firearm on "Cocked and locked"! Any trained soldier would not put his firearm away like that.