A person’s experience of hiccuping begins in the womb: fetuses hiccup before they breathe. Hiccuping continues as an inconvenient aspect of human life for years thereafter, but it is not only humans who hiccup: many other animals get hiccups too.
While the causes of hiccups vary, most cases arise from a disruption or irritation of the diaphragm, a thin sheet of muscle below the lungs. The irritated diaphragm sends a message to the brain via the vagus and phrenic nerves that causes the muscles of the diaphragm and other organs associated with breathing to contract spasmodically. This convulsion forces air into the lungs, and this push of air forces the air passage to close rapidly at its end, the epiglottis.
Hiccups can happen in any animal that has a diaphragm as the separator between the organs of breathing and the organs of digestion, and this includes all mammals. Other warm-blooded animals hiccup, just as humans do, when the diaphragm is somehow irritated, but because the physiology of animals is different from that of humans, the hiccups they produce won’t necessarily sound the same. The word hiccup is onomatopoeic; it imitates the “hic” sound the epiglottis as it closes, and the “up” of the next breath. When other animals hiccup, the acoustic properties of their organs affect how these disruptions sound. Cat hiccups, which occur frequently during kittenhood and sometimes after adult cats eat quickly, are often silent. In horses, hiccups are called the "thumps," and are audible not in the area of the throat, but along the chest. These seem to be related to an electrolyte imbalance.
Because animals get hiccups when the diaphragm is irritated, it follows that animals lacking this breathing apparatus don’t hiccup. Birds, reptiles, and amphibians, which breathe using other means of muscular contraction, can’t hiccup. Yet hiccup-like behavior among some amphibians may explain why many animals hiccup, a phenomenon that serves no purpose among adult mammals. When an amphibian with gills, such as a lungfish, breathes, it sucks in water. The water would drown the animal if it entered the lungs, and in order to prevent this, the epiglottis seals shut until the water passes back out through the gills. The gulp this process produces is like a hiccup. That mammal fetuses, human and others, perform the same gulp before their respiratory systems develop, suggests that hiccups are a vestige of their evolutionary past. When animals get hiccups, it is a reminder of the transition their ancestors made between water and land. Further, the impulse to close the throat appears to be related to the suckling instinct, which allows mammal infants to take milk into their mouths while keeping it out of their lungs.
There’s not much to be done when animals get hiccups. Cures are no more effective among other mammals than they are among humans, and waiting the hiccups out, annoying as that may be, is the most sensible course in most cases. The universal exception to this are hiccups that suggest an underlying medical problem. If human or animal hiccups persist for an unusually long time, or recur frequently, a visit to the physician or the veterinarian may be a good idea.
