Instantly you are transformed from a beam of light into an electrical impulse, and flashed along the optic nerve from the retina to the brain. And all of this in a tiny fraction of a second. The lens focuses light through the vitreous humor, a clear gel-like substance that fills the back of the eye and supports the retina. Your nose connects to the back of your mouth through two tubes. The air you breathe in goes from your mouth and nose down to your trachea and into your lungs.
Objects give off tiny molecules of themselves into the air.
When this molecule-laden air goes up your nose, the molecules dissolve in the mucus of your nose, where they come into contact with special receptors. Each nostril has a membrane, and each membrane is only about the size of a postage stamp. The membranes hold millions of receptor cells, each of which are ready to send messages to the brain about the molecules stuck up your nose. The olfactory part of the brain decodes the many messages it gets, and lets you know that, yes, your feet are truly smelly. Your nose has hair in it that can block some of the stuff, but the most amazing part is the mucus that your nose makes.