Here is a fairly irrelevant optical illusion. Incidentally, I zoomed in and checked, and it is false that the squares labelled A and B are the same color.

On most weekday mornings, I am in the dance studio at about eight in the morning. Due to the position of the windows and the time of year, that is the time of day when the sunlight is most intense in there. When I walk into the room on a sunny day, I can see my shadow on the floor, my reflection in the mirror, the reflection of my shadow, and the faint shadow of my reflection.

That last one is the weird part.

How, I frequently ask myself, is that possible? How can my reflection cast a shadow? Shadows are caused when something is blocking the light, and my reflection can’t do that. It’s just an image, not a physically real thing, and besides, it’s behind the floor where the shadow is, and things that cast shadows are supposed to be between the light source and the shadow. So why, in that particular room at that particular time of day, does that particular reflection cast a shadow?

I could easily have spent a good deal of time pondering this question, but in these situations, it generally has seemed to be a better idea to ponder other things, like, for example, dance, which is what one ought to be pondering when one is in a dance studio. Thus, despite my confusion and curiosity, I hadn’t put much thought into the issue of the mysterious extra shadow, and I hadn’t figured out why it existed.

And then today, I realized what was happening. When the sunlight comes through the window and shines on the floor, on me, and on the mirror, the light that hits the mirror reflects off of it. That sunlight has therefore become mirrorlight, and it heads towards the floor to join the sunlight already there in a joyous reunion of all floorbound light. But some of the mirrorlight doesn’t get there because, you see, I’m in the way. There is thus a roughly me-shaped light hole on the floor, and, of course, light holes are more commonly known as shadows.

Thus was this puzzling mystery solved.