[ WP ] Fairies exist and live in a complex society and have an economy like humans . Some of them have a special job : to collect human infant 's teeth . Explain why that 's an important job for their society .

Widders smiled and scampered out from under the pillow, her paws making only a slight scratching sound against the hardwood floor as she made her way up the windowsill and out into the brisk, night air. Only once she had reached the relative safety of the wind-swept roof did she stop to examine her prize. 
 
 The tooth gleamed under the light of a half moon, and Widders smoothed her quivering whiskers with an idle paw as she pressed one large, fuzzy ear against its surface. The tooth hummed with a gentle song, a refrain that spoke of summer sun, and wood smoke, and the scent of rain. The song played over and over—the bark of a dog, a slice of light through a dusty room and, under it all, a tiny note of loneliness. 
 
 Widders chittered happily to herself as she cleaned the tooth with a scrap of clean linen. Magic made with memories was quite potent, and the teeth of children always held a bit of a soul—a bit of childhood itself tossed as the body made way for adult things. This made a good tooth extremely valuable, especially since the actual harvest of human children had gone out of general practice a long time ago. 
 
 Widders snorted at the thought and cleaned faster. Some of the Fae lamented the loss of their old ways, but Widders ’ s kind, who had always been considered small and weak, were quite adaptable. The changes of the modern world had been good for them, and their services were now in high demand. 
 
 Widders already knew that the Troll, who spoke in words like falling pebbles, would appreciate getting her greedy claws on this little prize, come Market day. 
 
 Slowly, and with great care, Widders slid the tooth back into the pouch she wore snugly against her side. It made a nice clinking sound as it tapped against a couple of cuspids she had collected earlier in the night. 
 
 Across the city, a dozen more songs called out to her, and she raced off, eager to trade bits of shiny human coin for something infinitely more valuable.
