It's from a science blog called Physics Girl.
Here's the link:
Another video from YouTube:
I copied the instructions on how to make your own mirror:
I haven't tried to make one myself yet.
Broken glass from dropping the mirrors can be dangerous.
A homemade mirror will show a line down the center where the two mirrors touch. For a perfect model I saw them selling for over $200! So much money for two mirrors attached together!