White colouration around mouth?

[finlayb97]

I have just noticed this white discolouration on my Mexican red knee and have no idea what it is? It's definitely not mites or anything - the best way I can describe how it looks it is like if you scratched metal with a wire brush

 

[Casey K.]

Dried fluids from meals I would say....whatever you feed it.....mine have that too, sometimes.