This delicacy is the nest of a swallow-like cave swift, a small bird of Southeast Asia. The nests are actually the dried spittle of the birds. The most prized specimens are almost pure white because the twigs, bits of leaves, grasses, and feathers they once contained have been removed. Darker nests are still flecked with some of these materials. Others that are even darker, almost red, are called blood nests, the color the result of iron in the spittle. Like other exotic dried foods, such as shark‛s fin, abalone, and sea cucumber, bird‛s nests require a good deal of preparation before cooking. They are sold loose and in boxes and should be stored in a cool, dry cupboard until using.