Hiccups are bursts of breathing in activity. The muscles we use when we breath in are the intercostal muscles situated between the ribs, and the diaphragm.
Why do we hiccup? After eating or drinking too much or too quickly, the stomach, which is situated right below the diaphragm, becomes distended and irritates it. This will cause the diaphragm to contract, as it does when we breathe in.
However, sometimes hiccups may occur with temperature changes or emotional situations. In this case, hiccups will occur because of a disturbance to the nerve pathways from the brain to the muscles involved.