Answer: Crocodiles

When it comes to getting the nutrients you need, digestion is no joke in the animal kingdom and, for many animals, the stronger their digestive system is, the better off they are. In some cases, like with vultures and great white sharks, the creatures evolved to have very strong stomach acid—there is a species of vulture (the bearded vulture) with stomach acid so strong it can survive on a diet of primarily bones.

In the case of the crocodile, however, the digestive trick isn’t having the strongest stomach acid around, but having a body that can produce the most on demand. Scientists have long known that crocodiles had an unusual circulatory system (they have two large aortas in their chest cavity that supply the lungs and stomach respectively), but only recently has the purpose of the dual system become clear. When crocodiles and alligators feast on their prey, their brain sends a signal to a special valve in their heart that restricts the flow of blood to their lungs and pumps a huge amount of blood to their stomachs.

This aorta switching trick allows them to then secrete stomach acid at a rate ten times faster than has ever been observed in any other animal. So why does the trick work so well? Carbon dioxide is a key component in the creation of gastric acid and, by forcing their bodies to hold onto more carbon dioxide (by shunting blood past the lungs), they have a ready reserve of it to pull from their bloodstreams and use to create more acid.

The final piece of the puzzle is, of course, why they evolved to secrete such a huge volume of stomach acid. Because crocodiles and alligators tend to snap up large prey, they need to quickly break it down in their stomach before it begins to rot and poison them—the surge of acid breaks down their meal quickly enough to keep it from sickening them.