So when I render, I'm getting issues with the mouths turning into a mass of shapes and not being smooth. I am a Novice so this could just be a simple solution but some help could be nice.
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I remember encountering this error many months ago and on a single frame, so I assume the conditions for it to happen are super specific. I don't remember being able to fix it, but as an alternative you can use the viewport render image/animation option since for some reason the error doesn't appear there, although you lose certain functionalities depending on what you want to do.
I apologize for the inconvenience, the best I can recommend for now is to play a bit with the mouth modifiers or its transformations (scale, rotation and translation) since some minimal changes to these can solve some problems with the booleans it uses.