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A cough is a sudden, often repetitive, spasmodic contraction of the thoracic cavity, resulting in violent release of air from the lungs, and usually accompanied by a distinctive sound. A cough is usually initiated to clear a buildup of phlegm in the trachea; air may move through this passage at up to 480 km/h (300 mi/h). Coughing can also be triggered by a bolus of food going down the trachea instead of the esophagus, due to a failure of the epiglottis, although this may result in choking instead. Frequent or chronic coughing usually indicates the presence of a disease.