"The brain, when faced with a lot of stimulation, only some of which is considered relevant, will tune out the non-relevant parts, filling in what it can from the general area. It's a little like how the blind spot works, except this is a dynamic process. The brain will zoom in on a desired area, and the rest of the space will fade away. This is called the Troxler Effect, or Troxler Fading. It was discovered way back in 1804 by Ignaz Troxler, a physician and philosopher."
- An Optical Illusion that Explains the Origins of Imaginary Monsters.
They forgot to discuss the hypnotic and trance angle. Particularly that when certain games, like Bloody Mary, are played then there is an emotional charge to the atmosphere. In fact, that is far closer to mirror scrying than many realize. The primary difference is that the magician is knowingly manipulating the atmosphere to match that of the spirit that he wishes to use the Troxler effect to see. The ritual, the use of psychoactive substances (such as many incenses), and ensuing trance state and 'aberrant' (it isn't, really) way the brain is functioning all allow for the ensuing scrying or evocation.
Incidentally, it works just as well with locations. Don't ask me why.
And really, you don't need a mirror. You could just as easily learn to scry internally, or using a bowl of water, or a freaking fingernail. Although I have never managed that last one, at all. I keep trying, though...
[EDIT]: Oh yeah. And the circle with the dot at a center? Wherever have we seen THAT before?