A Doorframe Shadow Trap

The hallway light beamed a sharp, bright rectangle through the door gap right onto the carpet. An unmistakable parallelogram! I found a fat plastic highlighter and an empty matchbox, then stood right in the beam to cast my own dark shape. One step left, shadow stretches. One step back, it shrinks! I pushed the matchbox into the exact point where my shadow head met the baseboard. Perfect alignment. When someone walked down the hall outside, the light flickered off for two seconds and wiped out my polygon entirely. Gone! But the matchbox stayed put right on the mark.