There are over 100 physiological reasons as to what sets hiccups off,
the most common being expansion of the stomach and movement of
stomach acid into the oesophagus. After this then it could be an irritation of the thorax or the phrenic nerve (the nerve to the diaphragm). The mechanism of a hiccup usually involves a strong contraction of the diaphragm, the neck muscles and some other surrounding muscles. Just after the contraction begins we start
to inhale at which point the glottis (a kind of fl eshy trap door which
separates the food and air tubes in your throat) shuts off the windpipe
and this produces the ‘hic’ noise.
Scientists are still trying to find the actual purpose of hiccups. One theory is that they may have served useful for a common ancestor of ours. Standing on two legs gives us the advantage of using gravity to help digest our food, whereas four-legged creatures have to digest horizontally which means it’s easier for food to get stuck in their throats.
Some scientists think the lodged food could have hit a nerve responsible for triggering the hiccup allowing the food to be swallowed. If this is the case then hiccups could have been highly useful rather than just making you look daft!