“I feel like someone is watching me” is a classic horror film trope, but the idea also taps into a biological fact: Humans are good at sensing when someone is looking at them. While some label this gut feeling a kind of sixth sense, it’s really a biological phenomenon known as gaze detection, caused by a complex neural network in our brain. This detection system rests largely in our peripheral vision; the sense dissipates quickly when someone turns only a few degrees away from us. Because some 10 regions of the brain are involved with human vision, and little is known about gaze detection generally, scientists haven’t pinpointed what’s controlling this seemingly uncanny ability — although researchers have detected a dedicated group of gaze-detecting neurons in macaque monkeys.

Carrots are good for your eyes.

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You may have heard that carrots are good for your eyes. While this root vegetable won’t let you toss your prescription glasses, there is some truth to the idea. Carrots contain beta carotene and lutein, antioxidants known to prevent ocular damage by free radicals.

Gaze detection is particularly interesting in humans because our eyes are unlike any other in the animal kingdom. The area around the pupil, known as the sclera, is very prominent and white, which makes it easier to discern in what direction someone is looking. The overall theory as to why humans are so good at gaze detection boils down to the evolutionary advantage of cooperation. Simply put, humans are social creatures, and the detection of subtle eye movements helps us work with others while also helping us avoid potential threats. But because of the evolutionary importance of knowing when someone is looking at you, our brains tend to oversignal that someone is staring at us, when they’re really not. So if you’re ever feeling a bit paranoid, blame your brain.

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No two humans smell exactly alike, because odor is a complex medley of aromatic influences that come from our environment, genes, and various secretions; all of these add up to what’s known as our volatile organic compound (VOC). Biological sex can also be a differentiating factor, as a 2023 study from Florida International University discovered. As part of the experiment, 30 men and 30 women grasped cotton balls for 10 minutes in hands that hadn’t been washed for at least an hour. Those cotton balls were then analyzed using gas chromatography and mass spectrometry to identify the individual chemicals that made up the various VOCs of the participants. Using a type of data analysis known as chemometrics, the researchers were able to identify the sex of participant based on their hand odor with stunning 96.67% accuracy. In other words, men’s and women’s hands seem to produce different odors. 

The bacteria that make body odor are good for you.

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Most human sweat is essentially odorless salt water, but when skin bacteria eat proteins in our sweat, they produce odor. Many of these stinky types of skin bacteria actually protect us from eczema, as well as from dangerous infections such as MRSA.

This aligns with a variety of evidence that humans have subtle aromatic differences. Diseases have particular smells (acute diabetes smells like rotten apples, for example) and diet can also play a role. One study even found that single males smell differently than their partnered counterparts, mainly due to differences in testosterone levels. As for our hands, this subtle chemical fingerprint could one day inspire new tools for forensic scientists to analyze crime scenes. But for now, our fragrant hands remain primarily an aromatic oddity.

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Bioluminescence, the strange biology that causes certain creatures to glow, is usually found at the darkest depths of the ocean where the sun’s light doesn’t reach. While these light-emitting animals seem otherworldly, the trait is actually pretty common — in fact, you’re probably glowing right now. 

The largest known bioluminescent creature is the anglerfish.

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While the anglerfish is perhaps the creepiest bioluminescent animal, the “largest” accolade belongs to the Dana octopus squid, with the biggest measuring some 7.5 feet long and weighing 130 pounds. Scientists think the squid uses its lights to blind prey in the dark ocean depths.

According to researchers at Tohoku Institute of Technology in Japan, humans have their own bioluminescence, but at levels 1,000 times less than our eyes can detect. This subtle human light show, viewable thanks to ultrasensitive cameras, is tied to our metabolism. Free radicals produced as part of our cell respiration interact with lipids and proteins in our bodies, and if they come in contact with a fluorescent chemical compound known as fluorophores, they can produce photons of light. This glow is mostly concentrated around our cheeks, forehead, and neck, and most common during the early afternoon hours, when our metabolism is at its busiest. At such a low level, human bioluminescence likely isn’t an intentional product of evolution as it is for deep-sea fish, fireflies, and many other animals. And most other bioluminescent creatures rely on a compound called luciferin (Latin for “light bringer”) — which humans lack — for their light show. Fortunately, we have unique ways of making light that are all our own.

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For generations, 98.6 degrees Fahrenheit (37 degrees Celsius) was considered the standard temperature of a healthy human body. It’s one of the most familiar numbers in medicine, taught in schools and repeated in doctors’ offices around the world. But recent research suggests that today’s average person may run a little cooler.

The 98.6-degree benchmark dates to the mid-19th century, when German physician Carl Reinhold August Wunderlich compiled thousands of temperature readings and established what became the accepted norm. His work was groundbreaking for the time, but modern scientists have since revisited the subject using larger datasets and more precise instruments.

A fever is always a bad thing.

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In many cases, a fever is a sign that the body’s immune system is doing exactly what it’s supposed to do. By raising its temperature, the body can make it harder for some pathogens to survive and reproduce.

A 2020 study from Stanford University examined medical records spanning more than 150 years and found that the average body temperature in the United States has steadily declined over time. The researchers concluded that a typical healthy adult today may have a baseline temperature closer to 97.5 to 97.9 degrees Fahrenheit, depending on age, sex, and other factors. That’s around a one-degree drop since the standard was established.

Why the change? Scientists believe it may reflect improvements in overall health. Compared with people living in the 1800s, modern populations experience fewer infections like gum disease and tuberculosis, thanks to advances in sanitation, nutrition, and medicine. That makes the gradual cooling of the human body a possible sign of how dramatically our lives have changed.

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