I have a long haired cat who will eat her own hairballs off the carpet from time to time. AUGH! It's so annoying! I've already had her in for surgery for a bowel obstruction (hairball) once. It's like she has her own version of pica or something--she's obsessed. Even when I shoo her away, she has to finish what she's eating before she runs, and she's right back at it in a few minutes.