Swallows have well-developed mucus glands in their throats, and their saliva can solidify into solids in the air, which is the main material for their nests.

The bird's nest is half-moon-shaped, shaped like a human ear, with a diameter of 6-7 cm, a thick base and a thin profile wall, and weighs about 5-15g.

The nest has neat periphery and rough interior, like a loofah net. The nutritional value is quite high.