You can write secret messages using fruit!

Dip your paintbrush or toothpick into lemon, orange, or apple juice and write your message on a sheet of paper. As the liquid dries, it will disappear.

Give your message to a friend and have her warm the paper with an iron or hold it close to a lightbulb and your writing will magically appear!

Note:
Use caution while warming the paper, and use adult supervision if needed.