Chances are she's staring at other parts of you to see how healthy you are. Y'know… muscles, facial features, etc… After all, she wants the best traits for her children, right?
Okay, Mr. caveman… Let's go ahead and think only of the women who are man-hunting (and I would venture to say most aren't) and are looking at men not as human beings but solely as possible mates. ('Cause that's how men look at women, right? :P)
Under those conditions, ladies are not staring at muscles or “parts.” If the question is who will be a good mate, who will be a good father, and whose children will stand the best chance of survival and success, those ladies are not looking at the body at all (unless it is hideously deformed), they are looking on what is covering it. A designer suit? A lab coat? A stained wife-beater? These are the thoughts of the man-hunting woman. Is he clean and well-dressed? Does he have a good job? These are the traits of modern survival.
I know that the only time I stare or ponder any “part” is why it is either deformed or placed on display (like in tights or something). In these cases, I'm not usually thinking about the size or health or how this somehow translates to love or fatherhood, I'm thinking “Why the hell is he wearing those godawful pants?”
But maybe I'm ignorant. Are humans really just walking around on display like cattle at auction?
What worries me is if you think this is what women think about, is that because these are thoughts you have about women? Because I make a natural assumption that other people (both sexes) think of the same kinds of things I do. If someone glances at me, I assume they might be wondering where I am going today, or if I'm wearing a watch so they can ask for the time, or deducing my day's excursion based on my outfit or my gait. I don't assume they are thinking “Well, the boobs are a 7 but the butt is a 3.”
However, I did find this survey
of physical attraction for the people who are sizing each other (or themselves) up for market. Although I find it a mostly sad commentary myself. Especially this part:
While 92 percent of men would have a sexual relationship with someone with a fantastic body but an average face, only 82 percent would date them.
Which is another reason, I'd rather not venture into the minds of men.