This is a spectacularly horrific method of execution that is intended to break the will of the victim’s allies. I don’t think it is currently used anywhere, but it wouldn’t surprise me to find that some of the most barbaric, backwater hellholes in the world would use such a tactic… except that cannons aren’t very common anymore.The visual illusion is easy. All you have to do is stare at yourself for around ten minutes, without removing your gaze from the mirror, and ensuring you pick a point to focus on. You can see the effects taking place even after about a minute or so of doing this. There are 3 components to that window.
The actual window to the outside. The middle pane. And the window that passengers can touch. That hole helps minimize the force on the exterior window that is created by the difference between inside and outside air pressures The tiny hole also keeps moisture from accumulating and fogging up that window. Which I would be drawing penises on.