I'd say he might be more concerned as to why everyone else around him has a blank firing device attached to the muzzle of his weapon and the guy in front of him doesn't. Maybe the guy without the blank firing device is just stupid and forgot to attach it, or maybe he going to throw a magazine of live ammo into the weapon and start working over those around him. You can't be too careful about those around you when you are dealing with an area that is hot with muzzies that would just love to infiltrate a unit and then do what he has to do to go see allah. (I intentionally left the "a" in lower case, as there is no god named allah and mohammad was a false profit.)
Isn’t that just a dust cover, like a rubber?
Or he could just be starin’ at the other guy’s butt.