My cat's behavior confuses me.?

[ashlynlong]

Recently, I have been taking care of a stray cat. It seemed a bit standoffish at first, but it warmed up quickly. Now she's very love able and not so shy. The only confusing part is, when I pet her, which she makes obvious that she wants me to, sometimes she'll turn around quickly and bite my hand, and sometimes she'll hiss too. If she wants me to pet her, why does she behave the way she does and is there any way or possibility she'll stop?