I'd like to fiddle more and give you some examples, but Windows has suddenly decided to treat this game as a virus and refuses to let me run it.
This is my "best guess" for trying to adjust the System Prompt for your scenario after poking at my local QWEN-2.5 AI on this. This assumes the "Digestion" stat is being tracked on the prey (in this case, the player) and not the predator (the NPC that has swallowed the prey).
Text to add to your prompt:
### Detailed Instructions
#### Digestion
- **Initial Value:** The digestion timer starts at zero.
- **Increment:** Each time a creature swallows another, digestion begins.
- **Decay:** Digestion decreases by 10 every action that does not involve swallowing.
- **Threshold and Effect:** Once the digestion reaches or exceeds 100, damage Health by 25 with each subsequent action.