HUMAN NOSE CAN RECOGNIZE more than a trillion scents. “Our olfactory system evolved…to discriminate very similar smells, like my baby from my neighbor’s baby, milk that’s still good from milk that turned bad. So those are very similar smells that only differ in a few components. So we evolved to be able to make those discriminations. And as a side effect of that we can discriminate all those other odors too.” Most people underestimate how good their sense of smell is. Richard Feynman used to take advantage of that with some clever parlor tricks.