What causes hiccups?

A very full stomach can cause bouts of hiccups that go away on their own. A full stomach can be caused by:

• Eating too much food too quickly.
• Drinking too much alcohol.
• Swallowing too much air.
• Smoking.
• A sudden change in stomach temperature, such as drinking a hot beverage and then a cold beverage.
• Emotional stress or excitement.

http://www.webmd.com/hw/health_guide_atoz/ut1404.asp

http://www.answers.com/topic/hiccup
  

While many cases develop spontaneously, hiccups are known to develop often in specific situations, such as eating too quickly, taking a cold drink while eating a hot meal, eating very hot or spicy food, laughing vigorously or coughing, drinking an excess of an alcoholic beverage, or electrolyte imbalance

http://en.wikipedia.org/wiki/Hiccups