WHY does a person hiccup?
Hiccups are the result of regular ("pulsating") activity of the diaphragm nerve, which causes the diaphragm to contract in powerful and violent movements.
The bottleneck of the diaphragm is the center of the hiccups. When you eat in a hurry, when quite large pieces of food pass through the esophagus, the vagus nerve is injured: it is pressed and irritated.
The sound that occurs is the result of a sharp closure of the vocal cleft.
