Starla has become obsessed with one spot on the bed. She shoves her nose as far down as it will go then starts growling and digging like mad. She's already torn holes in two fitted sheets and it's starting to tear up the top of the quilt-top mattress. We have turned that mattress upside down trying to figure out what she is looking for. She has never had an accident there and she's never been in the bedroom unsupervised. We've even tried the granix apple spray to try to get her to stop chewing on the mattress and sheets, and while that spray stuff worked for woodwork and books, it doesn't work for this. This is the only spot she does this in. Anywhere else she digs, she just digs, but this is frantic digging like she's trying to get to something. Any suggestions---other than getting a new mattress?