I have a 9 1/2 week old guinea pig. We got him at six weeks old. He always sort of nibbled on our fingers but we thought he was just looking for food, so we offered him a carrot, apple slice or treat. Now that he is older, he really bites! Have we done something wrong? Did we create a problem by feeding him when he was being held? If so, how do we correct this? I know it isn't malicious, as he was chewing on the zipper of my jacket today as well. Please advise! Thanks!