This takes me back to the time when I wanted to determine which of my two cats is the one who makes the first move in their daily game of shess (it's like chess, but both the colours are black/brown and you don't move pieces - you just place them) in the bathroom.

I hooked a webcam to an old netbook and downloaded an app which would take a picture whenever it detected motion.

What I didn't take into account was the mirror in the hallway which during sunset would reflect sunlight at just the right angle to hit the toilet bowl.

In the end my results were a time-lapse of the sun shining on porcelain, because the mirror was far away enough to make the sun's movement trigger the motion detection sensing done by the app.