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It’s hard enough for your doctor to diagnose your mystery rash, but it’s leaps and bounds harder for historians to make sense of history’s weirdest and most mysterious maladies. Even with updated technology and research, it’s difficult to really know what really happened 500 or even 100 years ago. And that’s not to mention some afflictions that still stump us. These five cases — from explosive teeth to a dancing plague — have been the source of scientific speculation for decades or more. Do you have any theories?

The Dancing Plague of 1518

In July of 1518, a woman in Strasbourg — now part of France, then part of the Holy Roman Empire — stepped into the street and started to dance. She kept going until she collapsed from exhaustion, then started up again. More people started to join her, and a week later, there were more than 30 dancers, unable to stop even when overexertion set in and they started hurting themselves. Local leadership thought the solution might be more dancing, so they brought in dance halls, musicians, and even professional dancers. The issue, predictably, got worse, and eventually hundreds of people were afflicted. Some died of heart attacks and strokes. Strangely, this isn’t even the only time this happened — just the best-known case.

At the time, doctors and clergy thought the culprit was demonic possession or “hot blood.” Modern theories include stress-induced mass hysteria or a psychoactive mold called ergot that grows on rye (and which some have also blamed for contributing to the Salem witch trials).

The Mysterious 19th-Century Exploding Teeth

In the early 19th century, modern dentistry was basically in its infancy, which may be why nobody knows what caused several cases of exploding teeth. In 1817, a Pennsylvania reverend had a toothache so bad that he was, according to his dentist, “boring his head on the ground.” The next morning, his tooth burst apart with a sharp cracking sound and the pain was gone.

One exploding tooth is strange, but this wasn’t an isolated incident. Three more cases popped up in America in 1830, 1855, and 1871, and a few were recorded in England as late as the 1920s.

In 1860, one dentist theorized that gas from tooth decay was building up and causing the teeth to explode. Modern dentists have suggested that it was an issue with the varieties of metals used for fillings at the time. Both are pretty unlikely scenarios, and the cause remains a mystery.

What Plagued Ludwig van Beethoven?

Composer Ludwig van Beethoven famously started losing his hearing in his late 20s, and although he kept making music for another three decades, his affliction caused some severe depression. His lesser-known ailments certainly didn’t help, either; in his early 20s, he developed severe gastrointestinal symptoms that lasted the rest of his life. Overall, his symptoms were bad enough that he hoped his malady would be studied after his death. He died at the age of 56 with damage to his liver, kidneys, and pancreas after contracting pneumonia. Historians have spent the last 200 years trying to figure out his underlying illness, suggesting everything from lead poisoning to syphilis to celiac disease. DNA analysis from locks of his hair hasn’t turned up anything conclusive (and has just created some more mysteries), but it did reveal a genetic predisposition to liver disease.

The Sleeping Sickness of the 1920s

In 1915 or 1916, doctors in Europe started seeing patients with a mysterious set of symptoms. The condition would start out as a headache, fever, and sore throat before declining into a bevy of neurological symptoms such as double vision or tremors. Around 1 million people eventually developed encephalitis lethargica, or sleeping sickness — unrelated to African trypanosomiasis, which is also sometimes called sleeping sickness.

Eventually, many patients became catatonic or developed debilitating movement disorders that would keep them institutionalized for the rest of their lives. Some patients were revived briefly in 1969 with an experimental Parkinson’s drug, but eventually the symptoms returned. After killing hundreds of thousands of people, the disease all but disappeared in the late 1920s. Around 80 cases have been reported since 1940, but since the diagnostic criteria varies, the diagnoses may be unreliable.

Water Allergies

This affliction is more modern — it was first described in 1964. Technically known as aquagenic urticaria, it involves itchy, stinging welts that erupt within a couple of minutes after the sufferer’s skin touches water. (Drinking water usually seems to be fine). Only 37 cases have ever been reported. Scientists don’t understand what causes it: It might be a response to some kind of toxin in the water, a sensitivity to the ions in water, or some kind of histamine response. There’s no cure, only symptom management (like applying petroleum jelly before showering).

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Today, riding an elevator is a mundane activity, but little more than two centuries ago, these mechanical contraptions were steam-powered, death-defying wonders. In the years since, these mostly unseen pieces of urban infrastructure have become a key part of what makes modern cities possible. Without them, a city’s upward trajectory would be impossible, and the design of our world would be unimaginably different. Here are six amazing facts about the humble elevator, from its surprisingly ancient origins to the many places it may take us in the future.

Greek Mathematician Archimedes Invented an Elevator in 236 BCE

The elevator is a surprisingly old invention. According to writings from the ancient Roman engineer Vitruvius (the same Vitruvius who inspired Leonardo da Vinci’s “Vitruvian Man”), the Greek mathematician Archimedes invented a primitive elevator back in 236 BCE. Archimedes’ contraption bore little resemblance to today’s people-movers: It worked via manpower, with ropes drawn around a drum that was then turned by a capstan, a large revolving cylinder often used to wind ropes on ships. Although the attribution was written after Archimedes’ death, the invention makes sense for the great Greek thinker, who was famous for his exploration of compound pulley systems. Elevators join the list of other surprising ancient inventions, including such wonders as the world’s first steam engine and the world’s first computer.

Before the Modern Elevator, Top Floors Were Undesirable

Today the most luxurious high rises are crowned with multimillion-dollar penthouses, but before the rise of elevators (pun intended), the most desirable floors were those closest to the ground. The first building to include elevators at the design stage was the 130-foot Equitable Life Building in downtown Manhattan, which was built in 1870. Society was slow to adjust to the elevator, and the building was designed to look like it had fewer floors than it did. Also, the insurance company that worked out of the building still occupied the “valuable” lower floors, while the custodian enjoyed the upper floors. The era of the penthouse didn’t arrive in full swing until the 1920s, when the decade’s economic boom brought a flurry of construction projects to New York City and other cities around the world.

An American Inventor Created the First Modern Passenger Elevator

A key part of the very first passenger elevator was invented by Elisha Graves Otis, who founded the Otis Elevator Company, a manufacturer still in business today. Otis invented a safety device that would prevent an elevator car from falling if the cable broke. Before Otis’ invention, elevators were dangerous contraptions primarily reserved for moving cargo in factories, warehouses, and mines. In 1854, Otis introduced his “safety elevator” at New York City’s Crystal Palace, also known as “Exhibition of the Industry of All Nations,” where he asked someone to cut the rope that was holding him up. Once cut, the platform dropped only a few inches before catching him. This enhanced safety feature helped sway public opinion by demonstrating that elevators could be a safe means of vertical transportation. Today, elevators are considered statistically safer than stairs.

People Once Trained for Years To Be Elevator Operators

Although Elisha Otis invented a safer elevator, that didn’t mean the device was foolproof. For decades, operating an elevator was considered a highly skilled job that required years of study in some parts of the world, such as Germany. In the late 19th century, elevators were operated using “shipper ropes,” and operators were trained on the precise timing of pulling these ropes to arrive at the right floor. A well-trained operator was highly desirable, since they made the difference between a smooth ride or a death-defying jumble of starts and stops.

Over the decades, the job of the elevator operator became increasingly automated. In 1887, American inventor Alexander Miles designed the first automatic elevator doors, after reading about several accidents involving people falling down elevator shafts. But it wasn’t until the 1960s — a little over a century after Elisha Otis introduced the first safety elevator — that automated elevator cars began to replace human operators entirely.

The Fastest Elevator in the World Travels Up to 67 Feet Per Second

In the early days, elevators could only travel at about 40 feet per minute. After some 150 years of innovation, the world’s fastest elevator can now travel 67 feet in a second (or around 46 miles per hour). This elevator is located in Shanghai Tower in China, which also includes the longest continuous elevator run, at 1,898 feet. Originally installed by the Japanese company Mitsubishi Electric in 2015, the elevator got an upgrade in 2016, allowing it to traverse a path from the second-level basement to the tower’s 119th floor in just 53 seconds. The elevator in the CTF Finance Center, also located in China, comes in a very close second, traveling at 65 feet per second.

German Engineers Designed a Sideways Elevator in 2017

Since their invention two millennia ago, elevators have done just two things — go up and go down. However, in 2017 a German elevator company began testing an elevator that can travel in any direction. Nicknamed the “Wonkavator” after the multidirectional elevator seen in 1971’s Willy Wonka & the Chocolate Factory, the machine was hailed as “the biggest development in the elevator industry” since the device’s invention. However, a sideways elevator is only the beginning of what’s in store for the technology’s future. Scientists (and sci-fi writers) have also hypothesized about the feasibility of a space elevator that can ferry future astronauts from the Earth’s surface to outer space — completely forgoing the need for expensive, pollution-belching rockets.

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Some colors tend to come and go as fashion dictates, but a few have been chosen by humans for very specific, utilitarian purposes. Whether it’s about leveraging the advantages or limitations of human sight, or just evoking a particular emotional response, civil engineers and designers have used color to shape our world in ways you may not expect. Here are the stories behind the colors of five everyday objects — and why these hues are perfect for their assigned tasks.

School Buses

Glimpse a fleet of buses parked at any U.S. public school, and you’ll notice they’re all the same deep yellow — and it’s been that way for nearly a century. In an effort to standardize school bus construction around the country, thus ideally making them both safer and cheaper to mass-produce, school transportation officials met at Columbia University in 1939 to discuss the universal color for these vehicles. Fifty shades were hung up on the walls, ranging from lemon to deep orange. The color that was finally selected — known today as National School Bus Glossy Yellow, or Color 13432 — was chosen because of its ability to stand out from the background. Education officials didn’t know it at the time, but Color 13432 is wired to capture our attention, as the shade stimulates two of the three types of cones in the human eye — sending double the transmission to the brain compared to many other colors. That’s one reason a big yellow school bus is just so hard to miss.

Green Screens

In the age of computer-generated imagery, the green screen is nearly as ubiquitous as the film camera. The technique using green screens, called chroma keying, has been around since the early days of film, but why is the screen green, exactly? Turns out, this verdant hue has more to do with human skin tones than the color itself. Most human skin is essentially some shade of orange, and because green (and in some cases blue) is far away from this hue, the color can be used by a “chroma keyer” to replace the background image without affecting the human in the middle. This also explains why meteorologists can’t wear green on St. Patrick’s Day, since they would “disappear” on newscasts; the chroma keyer would include their green-hued clothes along with the green screen.

Traffic Lights

Traffic lights today help motorists navigate busy intersections, but this helpful technology is actually a direct descendant of railroad traffic lights. Before the dawn of the automobile, railroads used the color red to mean “stop” because red has the longest wavelength in the visible spectrum — meaning it could be seen farther than any other color. This was (and is) especially important on the rails, because trains can take at least a mile to come to a stop. Initially, green meant “caution” and white meant “all clear,” but when some conductors confused starlight as an all-clear signal, green eventually replaced white.

In the very early years of the automobile era, traffic lights were only two colors — green and red. The first yellow light wasn’t introduced until 1920, and the three-way traffic light we know today wasn’t patented until 1923. Yellow became known as “caution” due to the fact that it’s the second-easiest color to spot, after red. Originally, yellow was also used for stop signs as it was easier to see the color at night, but the invention of reflective materials and non-fading dyes soon saw the spread of red stop signs throughout the country.

Surgical Scrubs

Walk into any hospital (or watch any medical drama), and surgeons are almost always wearing bluish-green scrubs. Because blue and green are far removed on the color spectrum compared to red, these cooler colors help refresh a surgeon’s eyes when operating on a patient (whose insides are essentially various shades of red). Because surgeons are visually focused on red-hued environments, glancing at a white background (the chosen hospital color of times past) can leave a ghostly green after-image, much like what your eyes experience after a camera flash. However, if the surrounding environment is green, then those after-images simply blend into the background.

Airplanes

Although today’s Boeing 737s and Airbus A320s can feature colorful airline logos, the majority of the plane is painted white — and that’s for a good reason. Because the color white contains all colors in the visual spectrum, it’s also the most reflective, which helps keep airliners cool, especially when taxiing on runways. Airplanes are usually cooled by air sucked into engines during flight, or by external units hooked up to planes at the gate. However, if a plane experiences a long delay on the tarmac and engines are idle, things can get toasty really quick. So airlines will use any trick in the book, including lowering sun shades, opening air vents, and yes, painting planes white, to help keep passengers in the cabin as comfortable as possible.

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You’ve probably heard that your fingerprints are unique, and that no one else in the entire world shares the same pattern of ridges as you have on your fingertips. This certainty is so absolute that fingerprints have been used as a means of identifying people for thousands of years — Chinese societies used them for this purpose possibly as early as 300 BCE. But beyond their individuality, fingerprints continue to be a mystery to scientists and are constantly being studied. That being said, here are a few facts we do know.

Your Fingerprints Contain Whorls, Arches, and Loops

Technically, the patterns of ridges on your fingertips are called dermatoglyphs, from the Greek roots derma (skin) and glyph (carving). Fingerprints are the impressions left by the dermatoglyphs, though people often refer to both the ridges and their impressions as fingerprints.

The ridges follow three universal patterns: loops, whorls, and arches. Loops are curved ridges that fall back on themselves in an elongated C shape, with the open ends of the C pointing either toward or away from the thumb. Whorls are ridges in concentric circles or spirals. Arches look like the contour of a mountain. Of the three types, loops are the most common (60% of fingerprints), followed by whorls (35%), and arches (5%).

It’s Almost Impossible To Change or Eliminate Fingerprints

Fingerprints don’t change pattern or naturally disappear over the course of a person’s life, and it’s incredibly difficult to get rid of fingerprints, as some famous criminals could attest. The gangster John Dillinger attempted to hide his identity by burning off his fingerprints with acid (it didn’t work). At least two other Depression-era murderers tried to obliterate their prints with knife cuts. All found out the hard way that it’s almost impossible to eliminate fingerprints on purpose. The ridges will eventually grow back into the same patterns.

However, there are a few scenarios in which someone may lack them. People with a genetic condition called adermatoglyphia are born without ridges in the skin of their fingertips, palms, or soles of their feet. Skin conditions like psoriasis and repetitive manual labor can also change or wear down the ridges. Some chemotherapy drugs cause hands to swell and blister, resulting in the loss of fingerprints.

Fingerprints Form Before You’re Born

Studies have suggested that genetic and environmental factors guide the formation of ridges on the fingers, hands, toes, and feet between the third and sixth months of fetal growth. Genes that control the development of dermal layers in these body parts seem to dictate the size, shape, and pattern of the ridges. The chemical balance in the mother’s uterus probably plays a role, too. All of these influences add up to the creation of a set of dermatoglyphs that is totally unique — even identical twins have different fingerprints. Though it should be noted that despite the fact that scientists have studied fingerprints for a few centuries, they still don’t agree on how they form.

The Function of Fingerprints Is Still a Mystery

Scientists also don’t agree on why we have fingerprints in the first place, but they have some theories. For decades, biologists assumed that dermatoglyphs evolved to give people a better grip on things. Two University of Manchester researchers tested this idea in 2009 by running hard plastic sheets over their fingertips and measuring the amount of friction. They found that their ridges actually decreased the contact area between the fingertip and plastic, reducing grip power.

More recent research has suggested that fingerprints improve our sense of touch. For a 2021 study, researchers at Sweden’s Umeå University recorded 12 participants’ nerve responses while finely textured cards were run over their fingertips. The responses revealed hotspots of sensitivity that matched the ridge patterns of the subjects’ fingerprints — supporting the idea that they enhance our tactile feeling.

Animals Have Unique Fingerprints, Too

One reason that scientists thought fingerprints helped our grip ability is that other primates who climb and hang on to trees also have them. Gorillas, orangutans, and chimpanzees have dermatoglyphs on their fingers and toes that are unique to each individual.

Koalas also have fingerprints that look remarkably human, even though humans aren’t related to koalas. Biologists believe their dermatoglyphs represent convergent evolution, in which unrelated organisms independently develop similar traits.