My stray has a hard belly... is that dangerous?

My stray cat I take care of has a very hard belly. He seems healthy: eats, drinks a lot of water, poops and pees (I think). However, in comparison to my indoor kitties, his belly is unusually hard. It feels a little rounded, and it's only the abdominal area -- his chest cavity is fit and lean.

He just got castrated, vaccinated, de-wormed, blood-tested for Felv/FIV (both negative) last Wednesday.

What could be the problem?

Asked by Baby on Nov 27th 2012 in Other Health & Wellness