Hi thebluewhale777. A hiccup happens when a muscle in your body called the diaphragm contracts involuntary . The diaphragm extends across the bottom of your rib cage and separates the contents of your rib cage (heart, lungs etc) from your abdomen. The diaphragm plays an important role in breathing since it is the contraction and expansion of this muscle that causes air to be drawn into and expelled from the lungs. However, a hiccup occurs when the contraction happens involuntary. This is followed a short time later with the closure of your vocal chords, leading to the “hic” sound.
Yes indeed! it’s really weird! And also really annoying! For me, it always happen when I laugh a lot, and then that causes more laughing, and then more hiccups, etc…!!!
Anyway, back to science and answering your question. Like Greig said, most of the hiccup happens when the diaphragm contracts involuntarily. So it’s really like a muscle spasm (kid of like when the lid of one of your eyes starts going crazy… has that ever happened to you? it happens to me pretty often…). That spams of the diaphragm cause a very fast intake of breath, and the ‘hic’ noise comes from when this intake is suddenly stopped by the snapping shut of your glottis. The glottis is like a fleshy trapdoor that separates the food tube from the air tube in you throat.
Ok. So what are they for? The truth is that we don’t really know. It doesn’t seem like they serve any clear function, except making us look stupid! Some scientists think that they happen because of some nerve malfunction. It could also be that they are useless now, but they used to be useful before we evolved to become human. A bit like the tailbone and the appendix.
One possibility is that, when we used to be four-legged animals, they were very useful because food could get trapped in the throat much more easily (now that doesn’t happen because we have gravity to help us move the food down to the stomach, but for four-legged animals the food has to move horizontally in the throat so it can get trapped). Some scientists think that when lumps of food used to get trapped that way, it pressed on a specific nerve that made the hiccup happen. The fast intake on breath caused a vacuum that helped ‘suck in’ the food (and happily the glottis shuts so that the food doesn’t end up in the lungs!!!).
We can actually see this happen in animals like dogs, who eat very fast and are also very prone to hiccups!
Already beaten to it, damn 5 hour time difference between the UK and Chile! But, short story is that it is an unvoluntary spasm of the diaphragm. A fancy way of saying that the muscle which controls the lungs goes haywire and tenses up without you sending a message to say it should.