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As soon as an actor in a movie or TV show starts rattling off a phone number, every viewer knows what the first three digits will be: 5-5-5. How did “555” become the convention for fake phone numbers, and are there any real 555 numbers? Let’s dial up some answers.

Why do TV and movies need the fake 555 numbers? Just ask anyone who had the misfortune of having the number 867-5309 how their life changed after Tommy Tutone's 15 minutes of fame. Apparently some tiny fraction of the population—we’re guessing a fraction that largely consists of adolescent boys—thinks it’s hilarious to call any number they see on the screen. To curb these nuisance calls, movies and shows have been using the fake 555 numbers since as far back as the 1950s. (In keeping with the old exchange-naming convention, back then it was “KLondike 5” or “KLamath 5.”)

It’s hard to pin down exactly how 555 became the go-to fake prefix for phone numbers. In the book Easy as Pi: The Countless Ways We Use Numbers Every Day, author Jamie Buchan speculates that the repeated digit may have made the combination memorable, which helped it gain traction. Buchan adds that since no major place names in the United States began with a combination of the letters J, K, and L (the letters assigned to the 5 key on a phone), the KLondike/KLamath prefix wasn’t exactly a coveted commodity.

Since the early 1970s there’s been at least one 555 number callers can dial and get an answer—555-1212 is a standard number that rings directory assistance. The rest of the 555 numbers have largely gained fame as fake numbers in movies and on TV. (The number 555-2368 has risen to particularly rarefied air, possibly because of the “2368” combo’s use in old phone ads. Dialing 555-2368 will get you the Ghostbusters, the hotel room from Memento, Jim Rockford of The Rockford Files, and Jaime Sommers from The Bionic Woman, among others.)

#### Real Fake Numbers

What you may not know, though, is that there are many more “real” 555 phone numbers. Since 1994, 555 numbers have actually been available for personal or business use. That’s when the North American Numbering Plan Administration started taking applications from people and businesses who wanted their own 555 numbers. Theoretically, these numbers would have worked from anywhere in the continent; dialers would be able to dial 555-XXXX and always end up with the same number regardless of area code. The hope was that if you needed, say, a taxi anywhere in the country, you could just remember one number that would always work.

Things didn’t work out quite so smoothly. People and businesses snapped up the 555 numbers —except for 555-0100 through 555-0199, which were held back for fictional use—but they soon learned that owning a phone number isn’t all that useful if you don’t also own a phone company that can connect the number. Phone companies protested that setting up these services would be wildly expensive; in 2003 Verizon told The New York Times that adding the nationwide 555 service to its systems would cost the company \$108 million. (Verizon did offer to hook up the 555 numbers for owners, but the same Times story noted that the service usually required a \$2,500 set-up fee per area code.)

Skeptics claimed that the phone companies were just dragging their feet so the 555 numbers didn’t sap cash away from 800 numbers. There may be some truth to that theory, but the 555 system still isn’t up and running in any meaningful way. The list of people and entities that own the numbers is a pretty amusing read, though. It’s mostly newspapers, hospitals, random people, and the state of Nevada.

# What's the Difference Between Cement and Concrete?

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
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This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

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# Why Do You Stop Feeling Tired As Soon As You Climb Into Bed?

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There are few situations more frustrating: After a day spent nodding off at your desk, on the train, and on your couch, you suddenly can't sleep the moment you crawl into bed. It's not that you aren't tired or have insomnia, necessarily. Like a curse designed just to torture you, the sleeplessness only seems to occur when you're in your own bed at home, a.k.a. the place where you'd prefer to do your sleeping.

Doing things that aren't sleeping in bed isn't the only way to develop conditioned arousal. If there are other factors keeping you up at night—like thoughts about your day, or that cup of coffee you had at 8 p.m.—they can lead to the same result. Your brain starts to associate being in bed with tossing and turning all night, so even if those mental and physical stimulants go away, the muscle memory of being awake in bed remains.

Conditioned arousal is a vicious cycle that can't be broken in one night. The only way to manage it, according to the American Psychological Association (APA), is to minimize behaviors that contribute to poor sleep habits and to reserve your bed for sleeping (though sex is OK, according to the APA).

If you're a nighttime scroller, browse apps in a different room before getting into bed, or skip checking your phone at the end of the day altogether. When you spend more than 20 minutes struggling to fall asleep in bed, get up and move to a different part of the house until you get sleepy again; this will stop your brain from strengthening the association between your bed and feeling restless. The results won't be instant, but by sticking to a new sleep routine, you should eventually train your body to follow healthier patterns.

Of course, combating conditioned arousal alone isn't always effective. In people with conditions like anxiety and insomnia, intrusive thoughts and genetic factors can prevent them from falling asleep even under ideal circumstances. In such cases, the help of a medical professional may be required to sleep more soundly.

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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