After lots more soaking and a bit of prodding, he managed to get his mouth open, and made a good show of stretching/re-aligning his jaws, so I now know for sure there's nothing left inside of his mouth, and he doesn't have mouth rot or anything like I previously feared. But he still doesn't seem to be breathing properly. While he was in the water, air bubbles would form around his nostrils, and I think he's partially using his breathing tube. I did get a bit of skin off of one nostril; it actually wasn't forming air bubbles until I took it off. Hurm.