See a handgun fall? Probably not. That's too fine a level of detail for you subconscious. Plus your brain "fills in the gaps" and what you think you see may not be accurate (if you're really expecting a gun, a cell phone looks more like a gun than if you aren't expecting a gun, etc.) Seeing a weapon fall is a pretty modern way to tell your opponent is out of the fight and your subconscious isn't looking for that. No, your subconscious is much more concerned with your opponent folding in on himself, spinning to flee, big movements like limbs collapsing or the body falling, etc. Things that were relevant in feet/fist/tooth combat. Then it alerts you conscious to check out that development, and then you might notice the gun has dropped. What you'll probably notice, though, is that the opponent is no longer presenting a threat.