Why do animals close their nostrils?

Animals close their nostrils to protect their respiratory system from water, dust, and other foreign particles. This behavior is common in aquatic animals, like seals, which shut their nostrils when diving underwater. Additionally, some land animals may close their nostrils to regulate airflow or during stressful situations to minimize scent detection by predators. Overall, closing their nostrils is a vital adaptation for survival in various environments.