Our puppy school "teacher" said it was because she was missing something from her diet. Couldn't see what myself as she loves chewing whatever she can get her hands on. Last year I caught her chewing the corner of my copy of Against All Odds by Lex McAulay (there was even a nice leather bookmark sticking out of it so why not that?!) but fortunately the damage was minor. Yesterday while doing the mowing I found Jodi's sunglasses with both lenses popped out and teeth marks on the lens and frames...in one of the kill zones surrounded by toy stuffing.