Every single day, we are disgusted. It just happens. We blanch at unpalatable foods. We feel revulsed by corruption and intolerance. We’re grossed out by snails, worms and cockroaches.

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And while most of us are content to live with disgust without trying to understand why it exists, there are compelling reasons to cozy up to our disgust and get to know it well, all of which are explored in Rachel Herz’s thoughtful and entertaining book That’s Disgusting: Unraveling the Mysteries of Repulsion. Herz, a professor at Brown University and one of the world’s foremost authorities on the psychology of smell, explains why a little disgust is good for body and mind.

Why is it important to learn about disgust?

I feel that disgust really taps in to all the things that make us human. It is about, I think, our ultimate fears. Disgust is about death and about our fear of death in kind of an unusual way. Unlike the tigers jumping after you—that’s fear—disgust is a lot more insidious. You look at something gory, or you hear something, or you read something and it brings up this baseness and reminds you that you can be squished like an ant under somebody’s thumb and that your mortality is finite and unpredictable.

I think that disgust, really, is most deeply about that. It teaches us about confronting basic fears. You’re disgusted at the worm or the maggot, not because you feel something about the maggot, but because of how you’d feel if it touched you.

Is there a useful form of disgust—one that’s worth cultivating?

That’s a great question, and I sort of have a problem with giving an answer. The most utilitarian aspect of disgust is that it can help us stay healthy, to keep us away from disease. We don’t want to be in contact with other people’s germs and their cooties, and unattractive and sick people and so forth are, or can be, disgusting. There is obviously some sort of survival benefit to being cautious in that environment.

But at the same time I’m also sort of against this theory of psychology which is called the Behavioral Immune System, which says that it’s OK to hate fat people and immigrants and whatever because they could be harboring diseases that you could potentially be vulnerable to, and therefore this is a kind of disgust/disease social antipathy that’s justified. I’m really strongly against that line, and I don’t believe there’s good evidence for it. So even though I do believe it’s about disease avoidance, I don’t like how it’s been twisted.

In the book, you use the homophobia-inspired murder of Matthew Shepard as a prime example of that.

This is again relating to death, because we want to believe that the world is stable and orderly—that we can predict what happens and the ducks are lined up in a row. And when something breaks a norm—like if we believe that homosexuality is wrong for whatever reasons, religious or otherwise—then the norm is broken and the stability of the world is broken, and that sort of threatens us at that deeper level. We want to eradicate all those possible threats. I think the thing with homosexuality being very bodily-based makes it even greater than other sorts of things that can be norm-breaking.

But I think that rage often tends to feel like disgust and vice-versa. In most cases, where there isn’t something visceral about the immoral act, people are really angry and not disgusted, but they say “disgust” because it sounds better. “Anger” doesn’t have as much punch to it as saying you’re “disgusted.”

Does disgust have a good opposite? Is it delight?

I would say desire, rather than delight. Desire is about being drawn forward—you are lured in. Disgust is about pushing away, if you just think about it in a very simple sense.

Another interesting thing about disgust is that people are actually attracted to it. There is this perverse dimension where we, in fact, desire disgust when we watch horror movies or crane our necks to see who is dead on the pavement after a car accident. Disgust isn’t only about “getting away from.” There’s a twisted side to it, where you want to get into it.

So, what disgusts you? What really grosses you out?

Worms! Number one. And I think that’s based on something that happened to me as a kid. We learn a lot from our culture—a lot of it has to do with idiosyncratic experiences. One woman told me she hates the smell of roses because the first time she ever smelled a rose was at her mother’s funeral. I have a story about worms from when I was a little kid that kind of sealed the coffin on worms with respect to being grossed out by them, and I’ve never really been able to get over that. Not that I’ve tried.