It is the oldest of the senses and arguably the most useful. Even the single-cell organisms that preceded us by eons possessed a form of smell and used it to appraise their environment. More immediately and vividly even than vision—which has become the predominant human sense—smell can alert us to danger, invigorate or calm us, seduce us sexually or stimulate our appetites.

Smell is also the most treacherous of the senses. It can sneak up on us and stick a dagger in our hearts. A few stray molecules of perfume drifting through the air—invisible, unexpected—can turn our lives upside down in an instant. Suddenly, heartbreakingly, it’s as if you’re there with her again, drawn by her scent into an aching reminiscence of everything attached to it. Her voice, her eyes, her skin.

Smell affects us this way because it’s more intimately and strongly linked to memory and emotion than the other senses, and because scent memory persists long after its visual and auditory counterparts have begun to fade. Vision, hearing, touch and taste get to us indirectly. They transmit information to the cerebral cortex, the part of the brain that gives meaning to our sensory input, by way of the thalamus, a kind of relay station that passes stimuli along to the appropriate corner of the cranium.

The nose, on the other hand, is hardwired—hot-wired—straight into the forebrain. Odors are picked up by receptor cells in the nostrils and from there speed without detour to an organ called the olfactory bulb. This connects directly to the limbic system, which regulates much of what we remember and how we feel. New research suggests that the bulb itself might even store memories, making the connection even faster and more intimate. No wonder a waft of perfume can teleport us so instantly and tauntingly.

I’m not sure how old I was when I first started paying attention to the way things smell. As a kid, I took my senses for granted, as most of us probably do. They were just there. In the case of smell, I figured out early on that some aromas pleased me (burgers on the grill, fresh-mown grass, wood smoke), others didn’t (sweaty gym socks, garlic breath, rotten eggs), and I thought no more about it.

Gradually, as I accumulated life experience, I started noticing the scent of things more consciously and associating aromas with memories. One night early in my romantic career I had a kind of olfactory epiphany, realizing how capricious scent memory could be. I had gone to bed with a tall, soft brunette at her West Hollywood apartment, where I found the intense odor of chlorine bleach on her just-washed sheets almost too distracting. I was suddenly back in the swimming pools of my childhood, splashing in the sun, far too young for romance. (When the sense of touch took over, that memory happily receded and my olfactory system stored better memories instead.)

I think my olfactory life began to bloom in earnest when I was in my mid-20s and starting to learn about wine. Wine tasting, I quickly figured out, is mostly wine smelling. Literal tasting is important to detect things like acidity, tannins and viscosity, but everything else comes through the olfactory bulb, even (or especially) the wine’s actual flavor. What wine lovers call “nose,” or the way wine smells in the glass, depends on thousands of sense references, most of which we don’t even know we have. Scientists believe the human nose is capable of detecting at least 1 trillion different odors.

These are what make malbec taste different from pinot noir and German riesling different from its California counterpart, and a lot of what disposes us to like good wine better than bad.

Describing the aromas of wine is difficult, however, and wine writers tend to get a little wacky in their attempts. Wines, if you believe the critics, smell like black cherry, red cherry, dried cherry, lemon peel, gingerbread, smoke, tobacco, creosote, coffee, leather, spring flowers, autumn leaves, damp stone, cat pee, manure. Some of these descriptors are nonsensical. I recently saw “salted nuts” evoked to describe the nose of a chardonnay; sorry, but you can’t smell salt.

Others make perfect sense. Wine aged in new oak barrels, for instance, often smells like vanilla because both vanilla and oak contain a phenolic aldehyde called vanillin. There’s a hint of geraniums in muscat because both the muscat grape and geranium leaves contain an aromatic compound called geraniol.

I tend to cut wine writers some slack, in any case, because an interesting thing about smell is that it doesn’t have much of a vocabulary of its own. We have unequivocal ways of describing what we see (blue, square, hazy), hear (soft, discordant, high-pitched), feel (firm, hot, bumpy) and taste (salty, sour, sweet). Most of our descriptors for aroma, though, are metaphorical: That smells skunky, grassy, fresh; like apples, pine needles, gasoline.

We each develop our own associations, of course. Skunky to me might be buttery to you. Where I find apples, you might find pears. The perfume that reminds me of a lost love could summon a crazy aunt or nasty boss in your mind. The garlicky aromas drifting out the back door of the Thai restaurant down the street might make you queasy while they just make me want to dig into a bowl of khao soi. And the pungent smell of chlorine bleach, quite reasonably, makes many people gag. But it sometimes still reminds me of swimming pools, and brunettes.

Read the Rest of The Playboy Symposium: On the Five Senses

I See What I Hear by Sacha Jenkins

Bring on the Vomit by Paul Feig

Touch is More Than Touch by Emma Koenig

Taste Takes Time by Marina Tweed