Do you know a metaphor where someone is fighting a monster in a cave, but the cave is the monster’s mouth?

I keep thinking that I used to see this a lot, but when I try to look for examples, I can’t find any. I’m not looking for a specific piece of media. I’m just wondering if this is as well-known a symbol as I thought.

Basically, the thing they thought was the monster is the monster’s tongue, and the cave — what the character believed to be an immutable, passive, neutral part of the world — is actually part of the monster and actively against them.

TVTropes’ page for a literal living cave has a “that’s no cave” link that goes to “that’s no moon”, which is when anything believed to be landscape is actually giant and alive.

I’m looking specifically for situations where this is used as a metaphor for the problem having much deeper roots than they thought, and for things that they take for granted being part of the problem.

Is this a parable that’s been used, or is it something my memory just hallucinated?