Imagining a predator that can't regurgitate their prey. They are biologically unable to. There's just something about the structure of their throat or their stomach that prevents the muscles from working in the opposite direction.
In endo scenarios; the prey is just stuck there! Forever! This is the strongest, most pure form of perma endo. The bellypet will never leave their home again. Stronger than just the predator "promising" to never let out their bellypet, stronger than any legal contract or clause that dictates the permanence. Social bindings can be broken easily by carelessness or by waning feelings. Biological bindings are a different matter entirely, barring something completely invasive like surgery (which I usually don't consider in my fantasies). When the prey is swallowed, the door to the outside world closes forever behind them. They will never see the light of the sun or breathe the clean air of Earth. But the real question is: did the prey know this going in?














