Fascinating but some of it went over my head (wasn't watching). Couldn't watch the videos but I skimmed the other material. I'd like to add a few points that I've mentioned in other posts and this is a good place to repeat it.
I think we are, due to our socialization, a little inhibited from seeing some things, in the sense that we think it isn't polite to stare and it isn't polite to look in certain places, at least not when someone's watching. Children tend not to have this inhibition, you probably know, but it isn't difficult to overcome as an adult. No doubt you've all had the experience of being given "the once over," although it probably wasn't someone trying to decide if you were armed. It is just that people's appearances send a whole bunch of singnals to other people (consciously or not) and strangers may be attempting to decode those signals, in a manner of speaking. There is often mention of people's appearances here.
However, to give that a twist, in line with one of the references, is that if you are actively looking for something, in this case, on another person, you could easily miss something just because your attention is focused. That sounds counter intuitive but if you are certain someone has a pistol concealed under their bulky sweater and are focused on seeing that, you might miss what's in his pocket. Or, if you are watching his gun hand, you might miss what he's doing with his other hand.
On the other hand, provided the object of your attention is not interacting with you or attempting to do so, and likewise if you are not "over focused," you can sometimes see little things you might have otherwise missed. For instance, I was once lounging on a blanket on the grounds of the Washinton Monument one 4th of July about 30 odd years ago, waiting for the fireworks, when a man with a coat and tie wandered by. This in itself would attract attention in a mild way but I noticed an unmistakable bulge just behind his right hip. I'm certain he was wearing a gun, almost certain to be a short barrel revolver and almost certain to be a policeman. I wasn't looking for anything like that but just the same, it practically jumped out at me.
And finally, I'd certainly agree that it's next to impossible to be in top form all the time, even if you go to the range every weekend.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.