Some people have this reflex and don’t even realize it’s a thing.
Some people will cough if they put something in one ear, a very small percentage will cough if something is in either ear. It is called Arnold’s ear-cough reflex.
via: Getty
You know the smell of rain, or disturbed soil? It’s a compound produced by bacteria called Geosmin, and the human nose is extremely sensitive to it. We can smell it at as low a concentration as 5 parts per trillion.