Sounds like poop to me too.

If it makes you feel better, Shayna, after fasting all winter, was down to about 1430G dry (from about 1575G at her peak before fasting for 5 months). She had eaten three medium rats and was "up to" 1600G. One big poop later, down to 1470G!

If Geno is about 500G dry, I wouldn't even begin to worry until he's down 7-10% of his weight, or closer to 450G. At 500G, he can go a while without eating. Just make sure he has access to clean water and continues to drink.

Good to ask the question, but seriously, I wouldn't worry yet!

Good luck!