Sylvester like to gnaw on the loose rope - he savages his post until it yields a loose end then he unravels it for dental floss
Not seen any rope in his poop, but then he always "goes" outside so I wouldn't.
I haven't heard any bad stories about ingestion of this brittle material, though. When I clean up after Sylvester, it's always short pieces I pick up, nothing that would tangle an intestine.
Do you use catnip on the trees to encourage scratching? Some cats prefer to eat catnip than play crazy with it, just a thought?