It's an oldie but a goody, the one about the two perpendicular polarizers and a 3rd one is placed in between at 45°. Surprise surprise light comes through. No surprise for me of course, I know the punchline. Alastair didn't and wasn't convinced that I was telling the truth so he did the experiment and found out I was. So how can vertically polarized light suddenly have a horizontal component, waves are complex so lets try forces. Here's a diagram.

• A vertical force
• can be represented by two perpendicular vectors
• the horizontal components of these forces cancel
• Let's polarize the force only allowing a pull in the red direction
• the blue one cannot take effect
• now there is only the red force there is nothing to balance it's horizontal component

Voila as the say in parts of Canada.