Swalot swallows a lot. According to the pokédex, Swalot has no teeth but can open its mouth wide enough to swallow a tire, where it can be dissolved in its acidic stomach. There’s lots of interesting science going on in this purple blob of a pokémon, so let’s talk about it!
There are a lot of animals in our world who don’t have teeth for chewing, so they swallow things whole: frogs, ducks, and most remarkably, snakes. A snake’s lower jaw actually has two parts, connected by tendons. This makes the snake’s jaw extremely flexible, and able to open extremely wide to swallow things that are practically bigger than it. (Check out this video to see it in action)
While that’s really cool, it doesn’t really help us understand Swalot. We have no reason to believe Swalot is a vertebrate at all, or even has a jaw bone. In fact, Swalot’s whole body seems incredibly flexible, and it is able to distort itself to swallow prey.
This is a lot less like an animal eating a meal, and more like a process called phagocytosis used by single-celled protozoans and a few other cells, including in your own body. In your immune system, white blood cells will often devour harmful bacteria using phagocytosis. Phagocytosis comes from the greek work “to devour”, and that’s a fairly accurate description of what it does.
During phagocytosis, the predator engulfs the prey by surrounding it with its body. The predator’s cell membrane wraps around the prey and fuses back together, sealing the prey inside its own body and creating a cavity known as a phagosome, essentially a new stomach. Other parts of the cell, called lysosomes, will then flock towards the new stomach, and release enzymes to digest the prey: stomach acid. As the prey digests, the nutrients are absorbed into the cell. Whatever is leftover, the waste, can be thrown away by simply parting the membrane again, opening the stomach out to the world, and dropping the waste out.
Creatures that use phagocytosis don’t have just one stomach. Instead, they essentially create a new stomach every time they need to eat. This stomach can be as big or as small as they want: whatever size it needs to be to dissolve their prey.
At first glance, Swalot might look too large to be a single-celled organism and use phagocytosis. But, there are plenty of single celled organisms that aren’t microscopic. The algae Valonia ventricosa, for example, is a single cell that grows several inches in diameter.
So maybe Swalot is a single-celled organism! Perhaps Swalot’s mustache is a kind of flagellum, which acts as a sensory organ to see/smell/detect chemicals like flagellum do in single-celled organism. It is pokémon, so the interpretation is entirely up to you. One alternative theory could be that Swalot is a colonial organism, like Trubbish (read here).