For the most part, the cilia that also line the cavity work to move the mucus down the nasal cavity to the pharynx where it can be swallowed. Not all of the mucus stays fluid enough to be moved by the cilia. The closer the mucus is to being in the nasal vestibule and near the nostril opening, the more moisture it loses to the outside air, and the more likely it is to dry out and become stuck.