# Why Is It 'Eleven, Twelve' Instead of 'Oneteen, Twoteen'?

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English number words are pretty logical after a point. From twenty-one to ninety-nine, the same principle applies: you say the tens place followed by the units place. But the teens are different. Not only does the ten (which is where the word teen comes from) come after the units place (10+7 is not teen-seven but seventeen), eleven and twelve don't fit in at all.

Eleven and twelve come from the Old English words endleofan and twelf, which can be traced back further to a time when they were ain+lif and twa+lif. So what did this –lif mean? The best guess etymologists have is that it is from a root for "to leave." Ainlif is "one left (after ten)" and twalif is "two left (after ten)."

So then the question is, why don't we have threelif, fourlif, fiflif, sixlif and so on? The answer has to do with the development of number systems over history. A long, long time ago, when the number words were first being formed, most people didn't have much reason to distinguish numbers above ten. In fact, some languages of primitive cultures only have number words for one, two, and many. So the basic number words up to ten formed first, then they were extended a bit with the –lif ending.

Maybe there was a threelif, fourlif type system, but 11 and 12 were used more often in daily life. Many number systems are based on 12 because it's divisible by the most numbers, and because you can count to 12 on one hand by using your thumb to count three knuckles on each of the other fingers. (We have the word dozen because 12 is so useful). If 11 and 12 are being used more frequently, the forms for them will stick, even when another system starts to develop.

You can extend that idea to other number words. We have more irregularities of pronunciation in the tens (twenty, thirty, fifty instead of twoty, threety, fivety) because we've been making everyday use of those numbers for longer than we have for two hundred, three hundred, and five hundred). Thousand is an old word, but its original sense was "a great multitude," a non-numerically-specific, but very useful idea. The words we needed earliest, and used the most frequently are usually the most irregular.

So the short answer is, we created words for 11 and 12 a long time ago by calling them "one left after ten" and "two left after ten." They were more useful to us than the higher numbers, so we said them more and they became a habit that we couldn't shake.

Kids always notice the weird bits about language better than grownups. Thanks to five-year-old Katie English for this fabulous question!

# What's the Difference Between Mold and Mildew?

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We’re all familiar with colorful spots of something growing in our showers and in other dark, damp areas in our homes, but you may not know what to call it. Is it mold, or is it mildew? What is the difference between the two, anyway?

Both terms refer to fungus, but as it happens, it’s a squares-versus-rectangles situation. Mildew is a type of mold. The term typically describes fungi that grows flat, on surfaces like the walls of your shower or window sills. There are also several types of mildew that are specific to plants—powdery mildew and downy mildew are parasites that grow on certain trees, flowers, and crops, for example. While mold might be a colorful green or black, mildew is typically white.

The word mildew originally came from honeydew, a term for sticky secretions aphids and other insects leave on plants, which people used to think came from the sky, like dew. Eventually, the word came to refer to the mold caused by the fungi that fed on these secretions.

Powdery mildew on maple leaves
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Most of the household growths we refer to as mold belong to just a few families of fungi species. According to the CDC, the most common indoor molds are Cladosporium, Penicillium, Aspergillus, and Alternaria. Household molds can be a variety of colors, from orange-brown to green to gray to black. (Note that not all mold that is black in color is the more toxic species we call “black mold,” or Stachybotrys.) In contrast to the powdery texture of mildew, molds are typically fuzzy or slimy.

In nature, mold can play an important role in the ecosystem, breaking down dead plants and leaves. In your house, those decomposition abilities aren’t quite so welcome. Mold spores fly through the air, and when they land in moist places, they start to grow—whether that’s on food, your ceiling, paper products, wood, carpet, leather, or elsewhere around your house—and in the process, destroy whatever they're growing on. Unlike mildew, most molds grow down into the surface of its habitat, making them more difficult to remove. In porous materials, mold grows into all the empty crevices, which is why it is often impossible to remove all the mold from ceiling tiles (or soft foods like bread).

Mold growing in a Nashville home following a flood
Martin Grube, FEMA // Public Domain

Getting rid of the unsightly growth in your damp bathroom is more than just a matter of aesthetics. Indoor mold can cause allergic reactions, such as a stuffy nose or itchy eyes, and can lead to infections for people with compromised immune systems. Some people are more sensitive to mold than others, and may experience more symptoms when exposed to it. Generally speaking, though, mold spores are everywhere, so you’re never going to live a totally mold-free life. Spores will come into your home through windows, doorways, ventilation and climate control systems, and via your clothing, shoes, and pets.

But there’s only one way to effectively inhibit mold growth at home: Get rid of the moisture. That means fixing leaks, getting better ventilation, and possibly running a dehumidifier, according to the CDC’s recommendations on mold.

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# What Happens to Films Selected for Preservation by the Library of Congress?

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On Wednesday morning, the Library of Congress announced its latest slate of movies selected for permanent safekeeping in the National Film Registry. As always, the picks varied widely. The National Film Registry’s class of 2018 includes Cinderella (1950), My Fair Lady (1964), Jurassic Park (1993), The Shining (1980), Smoke Signals (1998), and the animated short Hair Piece: A Film for Nappy-Headed People (1984), which was produced by Ayoka Chenzira, one of the first black female animators.

Originally established in 1988, the National Film Preservation Act tasks the board with selecting American films that are “culturally, historically, or aesthetically" significant. They can pick up to 25 per year, and the movies must be at least 10 years old. The National Film Preservation Board is made up of representatives from a number of industry organizations, including the Academy of Motion Picture Arts and Sciences, the Directors Guild of America, and the National Society of Film Critics. With the new selections, there are 750 films in the registry.

Selection for the registry is an honor, of course, but what does it mean beyond that? How does the Library of Congress, the U.S. legislature’s storage agency for documents and media, go about preserving movies?

According to Steve Leggett, program coordinator for the National Film Preservation Board, selection implores the Library of Congress to get the best possible copy of the film in its original format and store it in their vaults at the National Audio-Visual Conservation Center in Culpeper, Virginia. This ensures the film will be available to future generations.

For Hollywood movies, the process is usually pretty easy. “We simply ask the studio to donate a copy,” Leggett told Mental Floss in 2015. In some cases, that isn’t even necessary. The Library of Congress has more than 1 million films on file, many of them sent by studios or filmmakers for the sake of copyright registry. When the original Star Wars was selected in 1989, Leggett says, congressional librarians simply checked that the 35 millimeter print submitted with Lucasfilm’s copyright application was in good shape. It was, so no further action was needed.

For older and more esoteric selections like newsreels, silent films, documentaries, and early technical achievements in filmmaking, Leggett says the library often seeks out a copy from the community of preservationists. Universities, private foundations, and hobbyists that preserve old films might get a call from the Library of Congress if they have a good copy of a National Film Registry selection. In rare cases, the library will barter for the film, using redundant materials on its shelves. Other times, it will make a copy or pay the archivist to make a new 35 millimeter copy for them. The Culpeper facility stores nitrate prints, the original film stock for many early movies, in specialty lockers because the material is highly volatile and flammable.

Silent films can be tricky because studios often released, revised, and then re-released versions of the film. When one is selected, Library of Congress archivists collect as many aspects and versions of the film as they can, which might mean contacting several studios and archivists.

Of particular challenge in 2015 was the induction of Symbiopsychotaxiplasm: Take One, William Greaves’s quasi-documentary of his 1968 theatrical project staged in Central Park. The film was screened often through the years, as Greaves gained a cult following. It was released on DVD in 2006, but the National Film Preservation Act specified that the library should seek a copy in the original format, which it didn’t have. Leggett said Greaves’s 1968 original cut was “lost,” but the library worked with the late filmmaker's estate to create a new 35 millimeter version that resembled it.

The Audio-Visual Conservation Center itself, buried on a mountainside, has storage space controlled to stay cool and dry. “A film could survive for hundreds of years there,” Leggett says. He admits the audiovisual center wouldn’t survive a nuclear strike—in the event of World War III, the world might lose its best copy of Buster Keaton’s The General—“but it did survive an earthquake with all materials intact.”