Wesleye

The company below creates the 'magic' post card that, when you pull the tab out, colors the image seen through the window. How is this done?

http://www.directmailing.nl/DirectMail/Wisselbeeldkaart/Toverkaart.aspx

The Wadsworth Constant is an axiom which states that the first 30% of any video can be skipped because it contains no worthwhile or interesting information.