Difficulty: 4 of 10
I've already said that I've written puzzles before. Here's one of the easier ones.
This one requires a bit of background on how 3D movies work. Two images are projected on the screen, each using a different polarization of light. You are given polarized glasses where each lens has a different polarization. Each eye sees one of the two images, creating the illusion of 3D. A vertically polarized lens filters out all horizontally polarized light. If you turn that lens 90 degrees, it becomes horizontally polarized, and will filter out all vertically polarized light. If you put a horizontally polarized lens on top of a vertically polarized lens, no light can come through.
Let's say you're watching a 3D movie. Everyone is wearing an identical pair of polarized glasses. You find that if you close your right eye and look at your neighbor, you can no longer see his left eye.
Wait, that's wrong! Are his glasses backwards?
What is the most likely explanation? [This is based on a true story, and nobody's glasses were backwards.]
Can't figure it out? See my explanation of the solution.