mouth question...

[LLinz]

Just had Sneezy out, and noticed that his mouth was not totally closed.. I looked closely at it, and could see some black residue type stuff just inside his mouth... I tried to get pictures, but he is a very active snake that never stops moving! Other wise, everything else is fine, temps are good, he's as active as ever, but I am very concerned about this. My first thoughts are: mites? Mouth rot? Please help!