That potato salad sitting out in the heat too long is a recipe for food poisoning. Fortunately, you can get rid of the bad microbes you consume by vomiting. No so for frogs. If a frog eats something toxic, it can't eject its stomach contents. Instead, the frog throws up its entire stomach.
This is called full gastric eversion, and it's a little like dumping out your pockets. A tidy creature, the frog wipes the stomach hanging out of its mouth with its front feet to remove any stray bits. Then it packs the whole thing back into its body, where it will presumably stay until the next noxious tidbit is eaten.
People feel nausea before they throw up, probably, so they learn to avoid whatever made them sick. Of course, there's no way to know if a frog feels a little green before it turns its tummy inside out.
Frogs aren't the only animals that can't vomit. Others include horses, rabbits and rats – one reason rat poison is so effective. And some animals share the frog's talent for throwing up the entire organ. When a shark can't stomach what it ate or feels threatened, full gastric eversion allows it to avoid poison and evade predators.
Some animals do frogs one better. Sea cucumbers, chubby wormlike creatures related to sea stars, can poop out their intestines as self-defense to tangle up and frighten predators. They can even break off their guts to escape, a kind of self-amputation called autotomy. Intestines regrow quickly, and the sea cukes seem none the worse for wear.