Dave, I totally and completely believe everything that you and other are saying and reporting. I don't know any other way to say it but I repeat, Perception is not necessarily reality. Charles Dickens said it best. When Scrooge first encounters Marley's "Ghost", He (Scrooge does what so many do not do, he questions his own senses. Marley's ghost asks, "Why do you doubt your senses?" Scrooge scoffs that "...a little thing affects them. A slight disorder of the stomach makes them cheat. You may be an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of an underdone potato. There's more of gravy than of grave about you, whatever you are!" Later, more pointedly he says, "Humbug, I tell you! Humbug!"
Humans depend mostly on vision which is actually a series of still pictures taken at a rate of 8-10 per second which the brain knits together to PERCEIVE motion. That's why movies or TV images seem to move. It is also why the "Hand is faster than the eye". Even at that rate there is too much data so the brain filters and focuses. Magicians know this and have pretty girls in scanty costumes. The brain also focuses on motion. Why magicians have the girls in motion or move their hands and body to focus attention away from the real action. Experience teaches that light travels in straight lines thus if we perceive something in front of us we believe it is really there and 99.9% of the time it is, yet the atmosphere can bend light. I know that the air above a hot road is bending light yet I perceive a reflection of the blue sky on the road which becomes water in front of me. Driving down the road in the evening and looking at the moon racing through the trees I perceive it chasing me. Knowing it isn't does not change the perception.
24/7 the brain receives data from the senses. It grows accustomed to this and actually requires it. Humans in sensory deprivation tanks quickly hallucinate seeing/hearing/feeling/etc that which is not there as the brain supplies its own data. Quite simply, when data is not supplied by the environment, the brain fills in the gaps. A bit of cultural priming and a half-seen flickering shadow becomes a Ghost.
I've fired thousands of rounds at moving shadows in the treeline.