“Sharks are anything but a cavern on the inside, you’re just familiar with seeing into their mouths. Just past the gills, you encounter the bulk of the body and the body cavity is rather full of liver, muscle, and other organs.
So lets say you ended up inside a shark somehow, and that somehow it’s stomach was large enough to fit you whole. You’d die either of suffocation or drowning but lets say somehow you don’t.
At first you’re hanging out in the shark’s stomach thinking, “oh this isn’t so bad”, and then you start to feel your skin burning because the shark’s stomach is flooding with digestive acid and digestive enzymes that start to break down your body. Then the shark’s stomach starts undulating and contracting to break whats left of your now fragile, half digested body apart.
After you’ve been properly turned to chyme, the stomach begins to vacate and you’re pushed into the intestine where the bits of you that are useful are absorbed and turned into shark. The bits that aren’t needed right away get stored away as fatty tissue in the liver which helps the shark not sink too fast and the rest of you continues along to be pooped out of the shark’s cloaca.
Most of this shark poop is still carbon and nutrient rich relative to the open ocean, so what’s left of you gets taken up pretty rapidly by the microbial communities in the ocean. Any particles too large to be taken up and consumed will rain down to the bottom of the benthos as marine snow where it will be eventually broken down by chemotrophic bacteria in the sediment or buried until the tectonic plate it’s on subducts at a convergent plate boundary and it is forced into the Earth’s mantle.
If you make it to the Earth’s mantle, you could be there for a while but eventually you will return to the surface in some form, either in some inorganic mineral, or if you’re really lucky, you could be outgassed in a volcanic eruption and return to the atmosphere.
From the atmosphere it’s a 50/50 shot if you’re going to be taken up by terrestrial trees and plants or become algae in the ocean. Perhaps you re-enter by being fixed by a CO2 loving green algae, so now a little bit of you is algae. Which sucks because you’re about to get eaten again. and again. and again.
Until you travel up to the top of the marine food web and become a shark. Look at you apex predator! Except then you get fished out of the ocean and have your fins cut off to make someone’s soup. So now you’re a person again… until you go swimming and get swallowed by another shark with an enormously large stomach.”