WHAT is this my cat leaves behind?

My husband and I found a stray cat in bad shape; nursed him back to health, and before bringing him inside took him to the vet for the OK. I first started noticing these off white colored 'things' on the floor and didn't think much of it. Then I started to notice that after my cat was on the couch I would find one on the couch where he had been sitting...that is when I started thinking that they were coming from him and started to look for them. WHAT IS THIS? They are slightly larger than a sesame seed (if you crack open a sunflower seed, they are about as big as the seed inside the sunflower seed shell), look kind of like a sessame seed--off white in color; but hard, they feel almost like a wood chip. I started finding these 'things' about the same time I found this website and started reading about parasites; so I don't know if I am being paranoid, but I have come up with a theory that they are some kind of parasite or parasite egg that is coming out of my cat's butt. I don't find a whole lot of them; but find anywhere from 1-5 of them a day. WHAT IS THIS??? Please help!!! Thank-you!