Fleas come inside, too. They're pretty mobile. Sometimes they aren't too noticeable. . .get a cheap flea comb and run it through your pets' fur now and then, and ask the vet for flea meds if you find any (because if you see one, there are a hundred more hiding!). And, yes, it's normal that tapeworms don't always show up in the poop. They're sneaky that way. Just tell your vet that you need some meds for tapeworms.