And as these cilia actually move in a wavelike fashion, they can actually move those harmful things that get stuck inside the mucous. They can move these things back out into our larynx. And within the larynx, they can either go into the esophagus and into our stomach, where the acidity will kill that harmful thing, or they can be expelled via the process of spitting. So, once again, mucous membrane within the trachea, the bronchi and the bronchioles, as well as within our nasal cavity, we have specialized cells called goblet cells. So these cells secrete a substance that forms a very sticky and slimy mucous membrane along the pathogeways within which our air actually moves. Now, when harmful particles and agents move with the air, they can get stuck within this mucus membrane.