One of the world’s most expensive food items is made from bird saliva.
Cave swiftlets nest high up on sheer rock walls inside pitch-dark caves, where they build sticky nests out of their own saliva. Traditionally, these nests could be harvested only by climbing on ladders up into the heights of these caves, a difficult and fairly dangerous undertaking. Today the swiftlets are encouraged to build their nests in artificially constructed concrete nesting houses. Even so, the harvested nests still sell for as much as $10,000 per kilogram.
