It's commonly known that many animals are able to detect extraordinarily weak odors. The real mystery is how they can smell scents that are 1,000 times too weak to produce the chemical reactions necessary to make a scent signal.
From the chemist's point of view, our sense of smell shouldn't work as well as it does. When you smelled that wonderful dinner a few days ago, a marvel of chemical reactions was taking place in your nose. Scientists still aren't sure how we sense such a wide range of smells. It was while investigating this question that scientists may have stumbled across the answer to another question.
The receptors in our noses have to detect a certain number of scent molecules before they can trigger the chemical response that makes the signal that tells us we have smelled something. When air is drawn into your nose, an organ called Steno's duct sprays a fine mist. Scientists always thought this mist simply humidified the incoming air. Now they've discovered that the duct also makes proteins that grab onto odor molecules. Sprayed into the incoming air, the proteins collect odor molecules. Then, with their load of odor molecules, they settle onto receptors that trigger your sense of smell. As a result, even scents that are too weak to smell are concentrated by this ingenious system so that we can sense them.
Our sense of smell helps protect us, gives our food flavor, and adds richness to the experience of living. It's truly a marvel of our Creator's design.