几乎每一个人都有过打嗝的经历。不仅大人打嗝，小孩打嗝，甚至在妈妈腹内的胎儿也会打嗝。更有趣的是，小狗小猫也会打嗝。那么打嗝到底是怎么回事呢？我们看看下文的解释吧。

    When you hiccup, your diaphragm involuntarily contracts. (The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdomen. It plays an extremely important role in breathing.) 

    This contraction of the diaphragm then causes an immediate and brief closure of the vocal cords, which produces the characteristic sound of a hiccup. What actually causes the hiccup is difficult to say - in most instances, there is no obvious cause.

    Attacks of the hiccups seem to be associated with a few different things: eating or drinking too fast; being nervous or excited; or having irritation in the stomach and/or throat.

    In some extremely rare cases, the underlying cause of hiccups can be pleurisy (inflammation of the membrane lining of the lungs and chest cavity), pneumonia, certain disorders of the stomach or esophagus, pancreatitis, alcoholism, or hepatitis. Any one of these conditions can cause irritation of the diaphragm or of the phrenic nerves that supply the diaphragm - it's the irritation that causes the hiccups.

    Still, the cause of most attacks of the hiccups remains a mystery.

    hiccup: 打嗝

    diaphragm: 横隔膜 

    involuntarily: 不自觉地

contract: 收缩

abdomen: 腹部

cords: 声带

underlying: 潜在的，根本的

pleurisy: 胸膜炎

pneumonia: 肺炎

esophagus: 食道

pancreatitis: 胰腺炎

alcoholism: 酒精中毒

hepatitis: 肝炎