a) Not really a conscious thought, more of an urge really. In fact, I can't ever really really recall hearing any sort of words or anything like that.
b) It depends on the situation, if she is alone or with just a friend or two I will approach her deffinitely. However, if she is with a really large crowd then I will leave her alone, or if she is surrounded by dudes. I hate it when I am one of ten guys all competeing for the same chick all at once, it's a little ridiculous.