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Can People Really Smell Fear?

Fictional characters, and even real-life folks, often talk about animals and people—particularly snarling dogs and knife-wielding lunatics—being able to “smell fear” on people. No one ever seems to be able to describe just what fear smells like, though.

The lack of detail—Is it musty? Does it have a hint of vanilla?—leads one to think that the smell of fear is more metaphorical than literal. But scientific evidence suggests that fear might really have a chemical component that we sense through our noses without even realizing it. The matter is far from settled, though.

Right Under Your Nose

In 2009, a team of German researchers collected sweat from two groups of students, one where the sweat came from exercising on bikes and one where it came from the stress of waiting to give a graded oral presentation.

A third group of students, lying in fMRI scanners and wearing modified oxygen masks, then smelled air odorized by the two groups’ sweat. Asked about what they were smelling, the students didn’t even notice an odor in half of the trials. When they did notice they were smelling something, they were unable to tell the difference between the two sources and rated both as low in intensity, weakly pleasant, unfamiliar, and having no effect on their own emotions.

The brain scans told a very different story, though. After smelling the sweat of the students nervously waiting for their exams, the smellers’ brains showed increased activity in areas that are involved with empathy and processing social signals and the emotional states of other people. The sweat from exercise didn’t cause these same activations, suggesting that the nervous students’ sweat contained some sort of chemical signal of their anxiety that triggered a response in the smellers’ brains without registering as the sensory experience of a smell.

That same year, a pair of psychologists at Rice University collected sweat from different volunteers while they watched horror movies or slapstick comedies, and then asked other volunteers to smell the sweat while they looked at images of faces that switched expressions from happy to ambiguous to fearful. As the faces morphed, the volunteers were asked to indicate whether they thought the expressions were happy or fearful.

The smellers were more likely to judge the ambiguous faces as fearful after being exposed to the the horror watchers’ sweat than when they smelled the comedy watchers’ sweat or a control sweat. That behavioral change suggests that not only did the sweat contain some chemical signal that communicated emotion, but also affected people’s visual perception of emotions and biased them towards the one being communicated by the sweat (that second part is consistent with other findings that emotional cues from faces and voices can regulate each other).

Just last month, Dutch psychologists found evidence that fear-induced sweat not only biases someone who smells it toward seeing fear, but might also push them to feel it themselves. Volunteers either watched scenes from a scary movie or from Jackass, and their sweat was collected. People in another group were then exposed to the smell of one of the sweats while they took a visual test that asked them to find a target object on screens full of different items. While this was going on, the researchers recorded their facial expressions and tracked their eye movements.

The people who got the horror sweat made facial expressions suggesting fear or anxiety shortly after they were exposed to the sweat. The Jackass-sweat smellers, meanwhile, made disgusted faces. (This was determined by comparing their faces to “distinctive facial-muscle signatures” associated with emotions. For more on face reading, check out Paul Ekman and his facial action coding system.) The two sweats also appeared to have affected the smellers’ behavior, with the horror sweat smellers attempting to acquire more sensory information while exposed to the sweat by taking bigger sniffs and scanning more and fixing their gaze less during the visual exercise.

What the Nose Knows

What all this, and a bunch of other studies looking at the same sort of thing, suggests is that humans might not communicate by just sight, sound, and touch. Like other animals, we might also use chemical signals embedded in our sweat, and maybe elsewhere, to let each other know about our emotional states.

That has been a contentious idea for a very long time, with some people claiming “definitive evidence of human pheromones,” and others saying “no, not so fast.” While there’s a good amount of evidence for behavioral and physiological changes in people in response to “chemosignals,” no one has been able to nail down just what the chemicals are that trigger these responses, and how people detect them. The vomeronasal organ, which many animals use to detect pheromones, is present in some humans, but doesn’t appear functional. When scientists can find them in people, the genes that code for their receptors don’t seem to have done their job, and their sensory neurons have little or no connection with the central nervous system.

Those are two very important dots that need to be connected before the line between someone’s sweaty armpit and someone else’s schnoz can be drawn clearly.

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travel
Why You Should Never Take Your Shoes Off On an Airplane
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What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

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Big Questions
Where Should You Place the Apostrophe in President's Day?
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Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


Wikimedia Commons // Public Domain

Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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