Sniff, sniff, achoo! You know how miserable a cold can make you feel. But did you know that it's the start of a battle?Nasty germs called rhinoviruses attack the cells inside your nose. Luckily, your body doesn't take this assault lying down.While your nose works to blow the invaders out with sneezes and wash them out with mucus, your blood cells also move in to fight the rhinoviruses to the death. That yellow-green mucus that's part of a cold is...