You might already know this, but letting cats play with loose pieces of rope is kind of dangerous. My friend had a really expensive cat operation because the lil guy ate the entire rope and it screwed up his intestines.
My cat loves string, more than any other play thing. But I had to stop it when I found him with a, um... piece hanging out his butt. (And he actually chewed that one off at both ends, from a "fishing rod" toy.) Careful out there, friends of cats.