I have two older kittens, about 8 months now. A boy and a girl, both done. They were the only two in the litter and they are very friendly and loving both to me and each other. They are very close and neither seems particularly to be top-cat, they play, sleep and wash together. However, the boy gets very intense when he washes his sister, and nibbles/chews off all her whiskers. She allows him to do this, in fact seems to be enjoying it, but she now has no whiskers! Why does he do this and how can I stop him? Any help or advice would be greatly appreciated.