Claire lost a tooth on Christmas, and the tooth fairy, who was apparently caught off guard and didn't have any silver dollars or lose-a-tooth-on-Christmas special money on hand, decided that something pretty-looking and exciting should happen to the bill that was left under the pillow.
She reports that this is terribly fun to do and that she recommends it heartily. (Heartily. Hee.) She also notes that this would be fun to do when leaving a tip for someone.
She may have used this tutorial she found on YouTube.