A hiccup is an unintentional movement (spasm) of the diaphragm, the muscle at the base of the lungs. The spasm is followed by quick closing of the vocal cords, which produces a distinctive sound. Hiccups often start for no apparent reason and usually disappear after a few minutes. Rarely, hiccups can last for days, weeks, or months. Hiccups are common and normal in newborns and infants.