(Intro)

Michael: A particular smell, or taste, or the sound of a Nickelback song... In the right circumstances, any of these things might trigger your gag reflex -- or worse, your emetic reflex, otherwise known as an epic case of cookie tossing. For humans, gagging has been a very handy strategy for not choking to death -- especially for babies, who often literally bite off more than they can chew. And puking might not be pleasant, but it can be a useful way to get rid of bad stuff in your system.

But despite its usefulness, not all animals gag -- or vomit. But they do have other handy tricks to compensate. Spoiler alert: some of them are kind of gross.

Horses, for example, can’t really vomit, because of the way their digestive system is arranged. You’re probably familiar -- though hopefully not too familiar -- with how puking works in humans. It normally starts with a gag reflex, which constricts the back of your throat. Repeated constrictions then trigger contractions of your abdomen that force stomach contents back into your esophagus. This eventually propels your lunch out of your mouth and hopefully away from any friends or loved ones.

Horses can’t really do that whole forcing-food-up-the-esophagus thing, though, because of their esophageal sphincter. That’s the valve that makes sure food stays in your stomach once you swallow it, and it’s much stronger in horses. Plus, the angle between a horse’s esophagus and its stomach is a lot like a bend in a hose. Vomiting builds pressure on the stomach side, and to alleviate it you either have to unbend the hose by re-arranging the horse’s insides, or try to add enough pressure to force vomit through the bend. But in this case, odds are the animal’s stomach would burst before anything got into its esophagus. Which is why, for horses, ejecting toxins via the mouth is very rare. Instead, they flush them out the back door.

The vast majority of nutrient absorption happens in the horse’s intestines and colon, and diarrhea is a quick way to clear these organs before they can absorb something that seems dangerous. Rats also can’t lose their lunch, partly because of a similar valve problem to horses, and partly because their muscles can’t physically make the movement that would get food up their esophagus. Instead, a rat that thinks it’s been poisoned will try to cure itself by eating other things, a behavior known as pica.

Rats aren’t known for being picky eaters -- except when they’re nauseous. Given the choice, they’ll ignore soils and pebbles in favor of kaolin, a kind of clay. The more nauseous researchers make the rats, the more clay they’ll eat, and rats given anti-emetics -- medications that reduce nausea -- will go right back to eating rat food, otherwise known as pizza in the subway.

Clay-eating seems to be a rat’s attempt to self-medicate. Biologists still don’t know all of the details when it comes to how the clay helps, but the metal ions in kaolin bond well with some toxins -- meaning that the rat doesn’t absorb them. Then there are the animals that don’t necessarily need to vomit... but they can, if they want to. So they use it as a defense mechanism.

Turkey vultures are particularly good at this. Vultures eat rotten meat, which can contain hundreds of species of potentially harmful bacteria. So if they had to hurl to get rid of that bacteria, they’d hardly ever be able to keep a meal down. Instead, turkey vulture guts are extra acidic, which kills off most of the bad bacteria before it has a chance to hurt them. They’ve also evolved a tolerance for certain species of bacteria that can cause massive die-offs in other birds. Those bacteria help them with digestion now.

But turkey vultures are still physically capable of vomiting. They just do it on purpose. Aggressively. Up to 3 meters. It’s a super effective strategy. Most people -- and a lot of other animals -- hate being vomited on. Plus, turkey vulture vomit can be especially acrid and corrosive. A diet full of decaying animals will do that. So if you ever encounter an angry vulture, you might want to back away.

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