Rales, crackles or crepitations, are the clicking, rattling, or crackling noises hear on auscultation of (listening to) the lung with a stethoscope during inhalation. The sounds are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration. The word "rales" derives from the French word râle meaning "rattle".