I've just noticed a strange behaviour in my female budgie Belle which I have never seen a budgie do before. She is climbing onto the sides of her cage, and then chewing on her nails. I've seen budgies clean their feet before but she is actually trying to chew on the nails, and she insists on being on the bars of the cage while she does this. She's also started doing it while sitting on a perch, this doesn't look like regular foot cleaning. I'm worried she may hurt herself. Has anyone experienced this before? Should I be concerned?