In this photo, you can see the water in an alpine pond acting as a mirror and a window, superimposed on each other. This phenomenon is fairly common in everyday life when looking at glass windows–depending how you focus your eyes, you can either see a reflection or see through the window. This is also true for laptop and TV screens, where you can often see both your reflection or what's on the screen. By focusing your gaze differently, you'll see one aspect more than the other.
This is cool is because, up until now, I have been focusing on factors mostly external to the viewer--the angle of light, the angle of the object, the wind, the particulates in the water, the intensity of light, etc. But here is where we can begin to think about properties of the eye, the camera, and the brain.
In the picture above, you can clearly see BOTH the mirror and the window behavior of the water. However, when I was standing there, I could "flip" my perception back and forth between seemingly just seeing the reflection and just seeing the bottom of the lake. The question is, "Is this something my brain is doing?" or "Is it something my eye is doing?" Is this a filtering process or a focusing process? Or is it a bit of both? My hunch is that it's more of an focusing phenomenon, because my eye actually gets tired trying to maintain certain foci, but I wouldn't be surprised if there were also a bit of my brain doing some selective-attentioning process.
Anyway, my goal is to find a similar situation and then manually adjust the focus in my camera to see if I can make a photo switch from mirror to window just by adjusting the focus, and not any of the external factors.