The Immune System
Just think about it--viruses and bacteria and all sorts of other dangerous pathogens are EVERYWHERE. They're on our tables, our chairs, our doorhandles, and our shopping carts; they're in our schools, our kitchens, and in some areas of the world even our drinking water. These sneaky little minions have been trained by years of evolution to invade our bodies however they can manage to get in. They weasel they're way into cuts, nestle into our lungs when we breathe, or hide in that oh-so-tasty mayo-based whatever at a 4th of July barbecue. But then what? Obviously, we don't die every time we get a cold. But why not? How can we survive these molecular attacks?