When you are breathing normally, your diaphragm, a large, powerful muscle in your chest, tightens and relaxes to pull in the air and push it out. However, when organs near your diaphragm become irritated, they cause the diaphragm to contract suddenly in a kind of spasm as it takes in a breath of air.
At the same time, the air passage to your lungs is closed off by a little flap of tissue called the epiglottis. So, when the air hits this closed-up passage, you feel a “bump” and then hiccup.
Hiccups may occur 2 or 3 times a minute or even 2 or 3 times a second. Most go away if you breathe deeply or hold your breath or even breathe into a paper bag. But scaring away hiccups with a surprise “BOO!” is just a superstition.
A man who first started hiccupping in 1922 was still hiccupping 10 years later.