We have stereo smell to help with locating smells. There’s also the nasal cycle. One nostril/sinus handles most of the airflow, then they swap (the sinuses are separate until they get to the throat). That way one can recover moisture, plus some smells are more easily detected with fast airflow and others with slow. So the nostrils functioning differently gives us a broader range of odor detection. What else? Umm, bilateral symmetry and redundancy is useful.

The same reason we have two eyes and snakes have forked tongues.

This guy nose.

If you do enough cocaine, you can end up with one nostril. It happened to a British TV celebrity in the 90s.

This guy nose.

We have stereo smell to help with locating smells. There’s also the nasal cycle. One nostril/sinus handles most of the airflow, then they swap (the sinuses are separate until they get to the throat). That way one can recover moisture, plus some smells are more easily detected with fast airflow and others with slow. So the nostrils functioning differently gives us a broader range of odor detection. What else? Umm, bilateral symmetry and redundancy is useful.

… So the snake can lick both our eyeballs at the same time before biting us on the nose?! Also two snake fangs, two human nostrils, aaahk it’s twos all the way down!