What you need
• A lemon
• A knife
• A small bowl
• Water
• A teaspoon
• A toothpick
• A sheet of white paper
• An iron

Steps
1. Cut a thin slice of lemon and squeeze the juice into the bowl.
2. Add a few drops of water and mix well using the teaspoon.
3. Dip the toothpick in the lemon juice mix.
4. Use the toothpick to write your secret message on the sheet of paper. If your message is long, you may need to dip your toothpick in the lemon juice again.
5. Let the ink dry. What do you see on the sheet of paper?
6. Use a hot iron and run it over the sheet of paper a few times. What do you see now?

Describe what you see and explain why it happens that way.

(Adapted from Science Spy)