Nothing happens to the diamond.
Exits unbroken and this is a dumb thing to do.
The stomach cannot digest it.
A diamond is hard carbon and so acid in a human gut does nothing to it. Stone just there in the dark.
It goes through long bowels. Comes out like it entered.
It is rare but the men who swallow them usually smugglers. The diamonds stolen.
They drink water and wait for nature.
The man lives if the stone small and smooth. It passes.
A large stone probably stops in the gut. It blocks the way.
A well cut stone is nice but edges are sharp.
They cut the soft meat of the intestines.
The man bleeds inside.
A pool of blood in the dark. A fever comes.
A surgeon must cut the belly open to find the stone.
A man should not eat rocks. It is a bad death.