Guano mining at Rakang Cave in Thailand supplies a good income for a small village of about 15 families. Descendants of these families have extracted guano from the cave for over one hundred years. With light only from small kerosene lamps, they briskly sweep the guano into baskets and later into bags. One or more miners sleep in the cave's entry room each night to guard the treasure within. This scene, and many more, can be seen in the upcoming one-hour CBS documentary, "The Secret World of Bats."