Your nostrils are extremely important, since they provide a direct connection to your lungs — for air — and your olfactory nerves, which your body uses to smell things. You are almost certainly aware of your two external nostrils, but you may not know that you've got two more, inside your head at the very back of the nasal cavity. Most animals have nostrils, even fish — though they use theirs only for smelling, not for breathing. Fittingly, the Old English source of nostril, nosðirl, translates to "the hole of the nose."