What's up with this baby's mouth?

[Lolo76]

I have one baby from my late-August clutch (of 6) who still hasn't eaten, but is surprisingly spunky & holding his hatch weight @ 52g. Recently I noticed a weird thing on his chin, and wondering what it is... also thinking it could be connected to his feeding issue. It looks almost like a water blister, right where the egg tooth would have been. The inside looks a bit dark but otherwise normal, and he flicks his tongue like any other snake. Here are some photos, and I'd appreciate thoughts on what's going on:

Luckily he's very photogenic, LOL.




See how it bulges a little?




P.S. I keep him in a 6qt Sterilite tub with flexwatt, and until last week I had him on paper towels... just switched to Carefresh (for added security), but I noticed the mouth thing before then.