The characteristic sound of a hiccup. Sometimes the only symptom is a slight tightening sensation in your chest, abdomen or throat that precedes the sound.Hiccups can be described as brief. The diaphragm regulates breathing. When your diaphragm contracts, your lungs take in oxygen. When your diaphragm relaxes, your lungs release carbon dioxide.The diaphragm contracting out of rhythm causes hiccups. Each spasm of the diaphragm makes the larynx and vocal cords close suddenly. This results in a sudden rush of air into the lungs. Your body reacts with a gasp or chirp, creating the sound characteristic of hiccups.