The Asian swiftlet is a tiny bird that lives in dark caves in Southeast Asia. Unlike most birds, this one makes its nest from its own saliva, which hardens when it is exposed to air. People collect these nests and sell them to restaurants where they are cleaned and served in a broth. The hot broth softens the hardened saliva and is a delicacy in Asian countries. This soup doesn’t come cheap though! A pound of nests sells for around $900-$ 4,500 (£540- £2,725)!