Coin flipping is a time-honored tradition for making decisions. Long before the NFL used the method to determine opening kickoffs, Romans employed coin tossing to settle personal disputes (though they called it “heads or ships,” a reference to the Roman coin’s two-faced Janus on one side and prow of a ship on the other). While the logic of coin flipping is simple enough — guess a side and flip — the physics of how a coin flips are anything but. By exploring this complicated motion, scientists have discovered that coin flips are not as random (and thus impartial) as most of us think.

The Wright brothers decided who’d fly first with a coin toss.

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On December 14, 1903, Orville and Wilbur Wright flipped a coin to decide who’d be the first pilot of their eponymous flyer. Although Wilbur won, his luck didn’t last — his flight attempt failed, allowing Orville to soar into the history books three days later.

A 2023 study from the University of Amsterdam flipped 350,757 coins across 46 different currencies and discovered that a coin flipped to its starting position 50.8% of the time — close to 50/50, but not quite. In other words, if a coin started heads up, there was a slightly greater chance it would land heads up, too. This supports a previous theorem, developed in 2004, which argued that coin tosses landed as they started about 51% of the time. This small difference likely won’t dissuade humans from practicing the coin flip tradition, however. A more serious concern comes from a 2009 study, which revealed that coin tosses can be easily manipulated with just a few minutes of practice. So if you’re relying on the “randomness” of a coin toss to determine important decisions, make sure you trust the person doing the flipping.

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The average adult blinks about 15 times a minute, whether to lubricate the eyes, clear unwanted irritants, or refocus attention. Babies, on the other hand, blink far less often — only two to three blinks per minute on average. So, why do infants blink less than adults? The answer may lie with our brain’s dopamine levels, which control human blinking. Scientists initially made connections between this feel-good neurotransmitter and blinking because people with schizophrenia, who usually have excess dopamine production, may blink more frequently. The inverse is also true — Parkinson’s disease, caused by damaged dopamine-producing neurons, makes people blink less often. So a baby’s infrequent blinking may be a clue about how the brain forms after we’re born, showing that a baby’s dopamine system is likely still forming and thus impacting blinking frequency. 

Birds blink just like humans.

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Like humans, birds have an upper and lower eyelid — but they also possess a third eyelid, known as a nictitating membrane. This transparent nictitating membrane sweeps sideways across the cornea, keeping it clean and moist. As a result, most birds don’t blink like humans do.

However, dopamine production is only one piece of the mystery. Scientists also theorize that because a baby’s eyes are small, they likely require less lubrication than adult peepers. Babies may also blink less often because it’s actually pretty demanding to be a baby, requiring more active attention to gather the necessary visual information for survival (and thus leaving less energy for blinking). So while babies may seem like pint-sized layabouts, they’re actually putting in a lot of work to become functioning and frequently blinking members of society. 

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Stargazers who live in major cities know all about light pollution, but this lack of complete darkness goes beyond geography. It turns out the sky is never totally black no matter where you live, even at night. We can mostly chalk this up to the luminous effects of moonlight and starlight, as well as to our atmosphere, which, in addition to making the planet’s air breathable, scatters all the light that passes through it. (This is what makes the sky appear blue during the day, as the atmosphere scatters blue light more than other colors.)

Water is intrinsically blue.

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Though it appears clear and colorless in small amounts, water naturally has a slight blue color caused by the absorption of light at red wavelengths.

In highly populated areas, the effect of light pollution is known as skyglow, and it’s what gives the night sky its milky, sometimes yellowish complexion. But even if you find yourself in an extremely remote location, the sky would be closer to a navy blue than black. As previously mentioned, this is partially because of the moon, but it’s also because the atmosphere itself emits a faint light of its own (in addition to the light it scatters), known as both airglow and nightglow. Depending on where you are, that glow could be any combination of red, green, purple, and/or yellow. If you’d like to see a completely black sky, you’d have to go to the moon, which has no atmosphere and thus nothing to scatter or emit light.

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It’s physically impossible to hum while pinching your nose. Go ahead, give it a try. See? To understand why humming, which we often associate with the mouth, would be affected by the nose, we have to look at the anatomy of our vocal folds. Vocal folds, aka vocal cords, are delicate bands of muscle located in the larynx, aka the voice box. When relaxed (i.e., when we’re quiet), our vocal folds resemble a wishbone. But when we speak, sing, yell, grunt, whisper — and, yes, hum — we send air up from the lungs and through the voice box. Simultaneously, those thin bands of muscle contract together, as if the open end of the wishbone has snapped shut. In reality, our vocal folds move in a wavelike pattern, vibrating against one another in varying frequencies that allow us to speak, sing, shout, and murmur. The faster our folds vibrate together, the higher the pitch; the slower, the lower.

We have “true” vocal cords and “false” vocal cords.

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“False” vocal cords, also known as the vestibular or ventricular folds, are thick folds of mucous membrane that sit above the “true” vocal folds to serve as backup protection against food or liquid entering the airway. Manipulating the “false” vocal cords can produce a deep, gravelly tone.

While we might think of humming as a sound that emanates from our mouth and lips, we actually produce this sound by sending air from the voice box to the nasal cavity and out through the nostrils. Thus, when we pinch our noses, there’s nowhere for the air to travel, and the vibration and corresponding sound stops. This also explains why pinching your nose mid-hum might make you feel like something’s caught in the back of your throat. (That’s the air trying to find a way out.) Another good way to test this theory is to hum when you’re congested. Depending on how blocked your nostrils are, you might not be able to hum at all, or you might even feel the mucus in your nose trying to move around as the air attempts to escape your nostrils — gross, but pretty interesting, too!

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