A fast gate at the entrance to the lungs
The vocal folds are two bands of tissue inside the larynx, or voice box, at the top of the windpipe. When liquid or another irritant touches sensitive tissue near the airway opening, nerves can trigger the folds to pull together. This protective response, called a laryngeal reflex, helps keep unwanted material from traveling down the trachea toward the lungs.
The closure can happen before a person has time to think about it. It is one part of a larger defense system: coughing can then help expel material that has reached the airway entrance.
Protection has a tradeoff
The reflex responds to irritation, not to whether something is “water” or “air.” The vocal folds form the passage air must use for breathing, so when they clamp shut, airflow can stop briefly too. That is why a small splash or a drink going down the wrong way can provoke a sudden choking sensation, coughing, or a short gasp as the airway opens again.
Usually the response is brief. If the folds remain tightly closed, however, breathing can be seriously impaired. The same gate that helps protect the lungs is useful only when it releases promptly; its split-second closure leaves no room for selective filtering.
