So, our skin creates a physical barrier that prevents pathogens from entering our body and attacking our cells. Now, if we examine the passageways inside our body, the air passageways, including the nasal cavity, the trachea, the bronchi, as well as the bronchioles found in the lungs, these air passageways are lined with a special type of mucus membrane. And this sticky and sliding mucus membrane is responsible for trapping the pathogens that enter our body through the process of breathing. And once these pathogens are trapped inside our mucous membrane, the cilia found inside the pathogeways carry those pathogens up to the outside of our body and sometimes into our stomach. And that leads us directly to number three fluid secretions. So, why would we want any sort of pathogen to actually enter our stomach?