I was wondering the same thing because my cats are all addicted to eating plastic, string, cardboard, hair, fuzzies, and the carpet. It really does make me wonder if something is missing from their diet- especially because of the carpet eating. It's non-stop and has completely ruined the living room. When they eat it, they literally rip the fibers up from the base and ingest them, later to be found vomited up somewhere else.