Illustration: Sam Woolley/Gizmodo

There was a time not so long ago when, for fun, or just for something to do, millions of Americans would tune in to watch non-actors eat worms for cash. It felt good, watching strangers wreck their intestines. Things might not have been going your way, but at least you weren’t competitively chewing cockroaches on primetime television.

In a sense the appeal of a show like Fear Factor was nostalgia—nostalgia, maybe, for the last iteration of our species, the one not yet trained, through wide-scale trial-and-error, to avoid eating mold, feces, etc.

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But what did that process of trial-and-error look like? And where did it land us? In other words: Which taste, at this stage of the evolutionary game, do we find most disgusting? Most of us, happily eating our for-the-most-part non-revolting salads and panini, have no reason, or desire, to think that one over—which is why, for this week’s Giz Asks, we’ve corralled a host of taste experts to do it for you. As it turns out, “disgust” is relative—yet another of the half-million interlocking social constructs which impede our desires, enrich various wealthy profiteers and, in this particular instance, prevent us from dining on diseased rat carcasses.

Richard Doty

Director of the University of Pennsylvania Smell and Taste Center

Disgust is a complicated issue in regards to taste. First, most tastes are actually smells. Taste buds only signify sweet, sour, bitter, salty, and savory (umami). We have many more bitter receptors than sweet or other types of receptors, presumably because poisons are often bitter alkaloids. However, when a “disgusting” agent is put into the mouth, molecules reach the olfactory receptors via the nasal pharynx retronasally. This is why coffee or chocolate have no taste when you hold your nose shut. This blocks airflow from the oral cavity to the receptors.

Concentration often is involved, with agents smelling or tasting fine at low concentrations but unpleasant at high concentrations. Context is also involved (skunk-like mercaptans can be pleasant at low concentrations but unpleasant at high concentrations, particularly if one is not told it is the odor of a skunk). Some dog anal sac secretions smell like limburger cheese. If you were told the odor was that of limburger cheese you would find it less disgusting than if you were told it came from the anal sacs of a beagle. Although perhaps not the most disgusting of all odors, pyridine was described by one subject in our lab as smelling like “puke in a urinal at a carnival”. I think most would find this a bit disgusting. The psychological responses of people to dog anal sac secretions, however, trumps pyridine in my experience.

Asifa Majid

Professor of Language, Communication and Cultural Cognition, Center for Language Studies, Radboud University Nijmegen

The idea of tasting someone else’s vomit or feces is likely universally disgusting. Generally, however, one person’s disgusting is another’s delicacy. The French and Dutch eat horses; but for most Americans the idea of putting horsemeat in their mouths is gross. Then consider the average American eats over 50 pounds of beef per year. Why would you ever eat something sacred that provides nourishing milk? The thought horrifies Hindus. Traditionally many Europeans eat pigs, but for the 1.5 billion Muslims in the world today, this is unthinkable. The list goes on. From coagulated blood, to caterpillars, sheep brains, tuna eyes, or baboon hands: somewhere it’s a treat; elsewhere it’s stomach-churning.

Perhaps we can find the most disgusting taste if we can test people before they become enculturated. Examining infants’ preferences provides interesting insight. Babies prefer sweet, salty, and umami tastes over bitter ones; and they avert their heads, wrinkling their noses, when presented with fish, garlic or rotten odors. However, should their mothers be avid garlic eaters, then garlic odors are no longer aversive to the baby. During pregnancy, the mother imparts the flavors she is imbibing via amniotic fluid to the baby. So babies already begin developing flavor preferences before being exposed to solid foods. Early exposure is so critical that it can literally make the rotten tasty. The Chukchi and Yupik peoples who traditionally lived in the Bering Strait region of Russia and Alaska ate food whose smell would make your eyes water. They would bury whole fish or tight rolls of walrus meat and fat into the ground and let it age and ferment for months, before eating. During the Soviet-era small settlements of indigenous communities were fused into larger culturally diverse communities, and during this time people abandoned these traditional foods. Then in the post-Soviet era, some people tried to go back to their traditional ways, but the foods that were so “tastily rotten” before were no longer such a treat. Without the early exposure to the pungent aromas, people found them inedible.

So what is disgusting to taste is as much about our culture, context, and upbringing as anything else.

Rachel Herz

Rachel Herz, is a cognitive neuroscientist on the faculty of Brown University and Boston College. She is in an expert in the senses and emotions that guide food perception and the author of The Scent of Desire, That’s Disgusting, and a new book Why You Eat What You Eat.

The most disgusting taste is bitterness. From an ecological and evolutionary perspective, being repulsed by the taste of bitter helps to keep us alive as things that taste bitter are high in alkaloids (pH greater than 7) which tend to be poisonous.

Everyone finds the taste of a lemon peel bitter but how difficult it is for you to eat it depends on the genetics that determine the number of taste buds you have. Supertasters have many more taste buds than non-tasters and everything taste more intense to them, especially bitter. If you can’t abide endive and Brussel sprouts you’re probably a supertaster and if you tend to order them as sides you’re likely a non-taster. Interestingly, how sensitive you are to bitter also influences your emotional reactions. Supertasters are less tolerant of pain and more easily angered and disgusted than non-tasters are, but non-tasters tend to score higher on traits that are associated with a psychopathic personality. A tantalizing corollary is that criminal psychopaths are much worse at recognizing the facial expression of disgust than any other emotion and also worse at it than other violent but non-psychopathic offenders. The hypothetical take home message—if you want to watch a gory horror movie with a friend invite the one who eats endive raw, but if you need someone to take you to the hospital you may want to call the friend who won’t eat kale.

Tim Jacob

Emeritus Professor, Cardiff University

Generally things taste disgusting because they are harmful or poisonous. But there is another quite different and personal aspect to disgust, involving conditioned association. If a food is eaten before or during a really negative experience it can become disgusting to us. For example, people having surgery or chemotherapy are often given a surrogate meal before the start of the process. This is because we can associate the pain, discomfort or sickness with the last meal we had so it is best not to have your favorite dish under such circumstances.

I had spam fritters once as a kid when I was coming down with flu’. There wasn’t a causal connection but my brain determined there was and forever after I’ve hated spam (which is actually pretty disgusting anyway).

Donald Katz

Professor of Psychology at Brandeis University who teaches behavioral neuroscience and studies what makes foods taste good or bad

Among neuroscientists, there is general agreement that there are only five tastes, of which only one is truly disgusting—bitterness. It stands to reason, therefore, that the bitterest available taste will turn out to be the most disgusting thing that you can (accidentally) put in your mouth.

I’d offer a specific recommendation…but if readers were to sample that recommendation, Gizmodo would find itself in a perilous legal situation. Bitterness, you see, fills us with disgust specifically because many naturally-occurring toxins are bitter. Thanks to evolution, critters that find bitter foods maximally disgusting are critters that survive, and therefore the most disgusting taste will be the taste that you taste once and then die.

Of course, despite what we scientists tell you, you know that there are many more than five flavors out there. Most of us can name five foods that are disgusting despite not being bitter, as well as bitter substances that we consider the opposite of disgusting; many people so love bitter coffee, in fact, that they will cast violent aspersions upon anyone who dares diffuse that bitterness with sugar. Where does this leave our search for the most disgusting taste?

The plurality of tastes reflects the mixing of multiple ingredients in any foodstuff, and the involvement of other senses in flavor perception (if you don’t think that smell and vision are important to flavor, try telling different Skittles™ apart without using either). The fact that one person’s dietary staple might be disgusting to someone else, meanwhile, reflects the experience-dependence of taste. Most animals are endowed with a mechanism, well known to over-indulging college Freshmen, that renders a non-bitter taste un-consumable, if that taste has proven toxic. My lifelong hatred of coconut stems from a Bad Birthday Cake Vomit Experience had when I was five years old.

This process works in reverse as well—foods that inspire feelings of well-being become favored, even if bitter. Teens learn to like beer and coffee because cool and/or sexually desirable peers like beer and coffee. Preferred bitter greens improve health. Licorice to the Dutch, vegemite to the Australian, natto to the Japanese; all substances that are disgusting to most, but rendered tasty by cultural acceptance.

And so what food “wins?” When you bring all of these factors together, what emerges as the worst-tasting foodstuff in the world?

It’s coconut. Trust me. It’s just nasty.

Do you have a burning question for Giz Asks? Email us at tipbox@gizmodo.com.