I have a female friend who told me that females have wider vision than male. This means that they can see relatively wider and lower as well than male. This also means that they can see, e.g. your shoes without lowering their head or tiling their eyes. She told me that they can check out guy's groin without guys noticing them.
Oh, and she said they will also know when you're looking at their boobs, even if it's for a split second.