rowe: so many behaviors are mediated by our sense of smell and by olfaction that uh it's-it's really one of the most important senses that we have. of course it's easy to take it for granted you know, and so whatever enters your nose, your nose has to figure out, "what is that? is it good? is it bad? is it dangerous? is it romantic? is it threatening?" sherman: why do we exist? i mean, we exist to have perceptions, and to have sensations, and to have experiences, and emotions, and really, the brain is where that all takes place. herz: smells do trigger our most emotionally intense memories. because emotion is so deeply intertwined neurologically with the experience of smell, we literally have this emotional response almost immediately upon smelling something. [music] host: our sense of smell is gateway to the seen and the unseen world and the key to our memory, our mood, and even our ability to lose weight. we take over 20,000 breaths every day that are filled with information that we largely ignore. but even if we aren't aware of scent, it is constantly giving us messages about the