The Diaphragm Muscle
The star of the hiccup show is your Diaphragm. This is a large, dome-shaped muscle located right below your lungs. It is responsible for helping you breathe by pulling down to let air in and pushing up to let air out.
Sometimes, this muscle gets irritated or 'glitches,' causing it to jerk downward suddenly and involuntarily.
Common Irritants
What makes a diaphragm glitch? Common triggers include eating too fast, drinking carbonated sodas, or even a sudden change in temperature. These things can irritate the Phrenic Nerve, which controls the diaphragm.
When the nerve is annoyed, it sends a rapid-fire signal that makes the muscle spasm.
The Slamming Door
The actual 'hic' sound doesn't come from your stomach; it comes from your throat. As the diaphragm jerks down, you take a very sudden, sharp breath of air.
To prevent this air from hitting your lungs too hard, your Glottis (the opening between your vocal cords) snaps shut instantly. The air hitting those closed cords creates the 'hic' sound.
The Tadpole Theory
Some scientists believe hiccups are an evolutionary leftover from when our ancestors lived in the water. Tadpoles use a very similar muscle reflex to gulp water over their gills while closing their lungs.