Losing a tooth can be a scary experience, so it’s no surprise that parents throughout history have created rituals to celebrate this rite of passage. In the United States, children who leave a newly lost tooth under their pillow know to expect a nocturnal visit from the Tooth Fairy, who might leave a shiny quarter, a new toothbrush, or perhaps even a crisp $20 bill! But how did this tradition begin, and what is a tooth really worth?