Hiccup reflexes and mechanisms, illustration. Hiccups are an involuntary set of spasms in the diaphragm and throat, resulting in a characteristic 'hic' sound. During a hiccup, the diaphragm (below the lungs) contracts, and at the same time the epiglottis (a flap of tissue in the throat) closes the windpipe (trachea). Some theories state that this reflex arc starts in the throat, while others state that the trigger is in the diaphragm. The function of the epiglottis is to prevent food entering the lungs.