I use a flea comb to find "flea dirt." You can distinguish it from regular dirt by putting the “dirt” on a wet paper towel. If the dirt spreads like blood, it's from fleas. Then I treat my cats with a product called revolution.
One of my cats swallows rodents whole. Other cats of mine have eaten only little pieces. So I'd find the intestines and a tail. Usually only in one spot, but cats are individuals so yours might stash a liver here and an ear there.
You are so right about formerly ferals! Mine is in my lap right now. She is seriously annoyed that I'm not gazing back into her loving/creepily obsessive eyes. I can't get that cat off my shoulders or lap. Its great to be loved, but she takes it to the next level. You'd never guess that I...
I have 3 inside cats. Two originals. One tamed feral. The "feral" has been inside the house for about 8 years now. One of the originals loves her. The other would like to eat her. We keep them separate when we are not at home.