Question: why do we have snot and mucus?

Maheen Siddiqui answered on 15 Jun 2016:

There are tiny hairs inside our nose known as cilia. They act as a sort of filter between our nose and our lungs. The job of these hairs is to trap dust, bacteria and other foreign particles from the air we breathe to prevent them from going into our lungs. Over a period of time as bacteria and dust accumulate, snot and mucus form.