Is it possible static electricity builds up in her fur when you pet her? My sister's long, haired black cat (Molly Poods) is what we call a "love biter". She will crawl into your lap purring like a storm and lie down for some snuggles. You can pet her 4 or 5 times before she bites a plug out of you. In the summer she's fine. If she's shaved, she's fine. We finally figured out it was static electricity "zapping" her and that's what she was reacting to.