Phlegm

Together with the cilia, the cup cells clean the respiratory tract. The mucus secreted by them rests on the respiratory tract and promotes on the one hand the humidification of the breathing air and on the other hand helps to transport the smallest foreign bodies from the respiratory tract.

https://de.wikipedia.org/wiki/Flimmerepithel

https://de.wikipedia.org/wiki/Becherzelle _{(Wikipedia CC-by-sa-3.0)}