And this mucus membrane essentially lines our passageways. And when we breathe in the air, these harmful agents and harmful things, as they travel through with the air, they can essentially get stuck inside this mucus membrane. And if we move on to number two, we also have these hair like structures that can essentially move in a wavelike fashion that are found along the cells that line our passageways. 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.