As others havce stated, it is very possible to have a digested mass block the anal vent. It can be palpated out, but if you have never done it before, I would definitely seek assistance from an experienced keeper or a veterinarian. Palpating without experience could lead to a prolapse, or if the intestinal tract is torn during the process, internal probelms could occur (i.e. septicimia, or other infections).

I have also heard of other knots or balls inside of animals that are undetermined as th what they are, but they do not seem to hinder the animals ability to eat or pass waste. A diagnosis by a bet is probably the best bet.

Hope that helps,