I was in my room folding laundry and kept hearing the sound of plastic cups falling. So I grabbed my camera and went to investigate.
Apparently this is what happens when you don't put paper products away from camping and they live on the counter for a couple of days. These cups are now on his computer desk in the play room and he can stack cups whenever he wants to.
Over and over and over again. It's pretty impressive how fast he can get them all stacked up.