random thought while reading more Twilight...

So, I started reading the second part -- though I'm not that far along yet -- and I really don't get how this vampire reaction to blood is supposed to work. Apparently even a little blood, like from a paper cut, taxes their control, unless they have lots of practice like Carlisle. Okay, whatever.

But how does that work while they are in a school where half the students will bleed three to five days per month?? Granted, it's not a lot of blood, but more than from a paper cut, so they must smell that. And it's not like they growl a lot at random girls from what I gathered. Is this explained somewhere? Did I miss something? Does menstrual bloood smell icky? What? I don't get it.