Optical illusion
You have to thank those teachers that will let you have at least a note sheet during the test. But sometimes, that single note isn’t enough, and no matter how small the font you use on it is, you cannot fit as much information as you would like.

But if you get creative, you might have a solution. Remember Spy Kids 3D? No? Well, we are pretty sure that you will still have its glasses around your house. They will help you obscure or highlight two layers of text written on top of each other. Remember to write one layer in blue and the other in red!