We adopted Cyrilla 2 weeks ago from the animal shelter. She is very loving, and playful. But quite often when I am petting her, she will suddenly grab my hand and start chewing on on a finger. I pull away and say "NO", then offer her a toy. She just cries and rubs up against me. This isn't just soft little nibbles, it's hard chewing. I have no idea what to do about this. I have had cats my entire life, and none of them have done this. What should I do?