Invisible Ink

1/4 cup lemon juice
cotton swab (per girl)
sheet of paper (per girl)
lamp with light bulb
1) Set the lemon juice where all the girls can reach it.
2) Have them write the name of another girl using a cotton swab for a pen.
3) Let the messages dry. You will not be able to read them when they are dry.
4) Turn on the lamp. After it has been on for a while, have the girls sit in one group.
5) One by one, hold the papers close to the light bulb.
6) After the name is visible, have that girl try to guess who wrote it. Explanation: Different things burn at different temperatures. The lemon juice chars at a lower temperature than the paper, so when the writing is held near the lamp, the lemon juice chars and becomes visible.