4. Why do we crave greasy food when we're hungover?

15 Answers To Things You've Always Wondered About 9
via Boston Foodie Blog
Almost everyone craves a big ol' plate of greasy food after a night of drinking, but why? It's high in fat, high in calories, and you'd probably never eat any other time. The reason behind this craving is a brain chemical called galanin, which increases your appetite for fats. Since alcohol increases your body's production of galanin, you're going to want that big fat breakfast pronto.

5. Why is the drinking age 21?

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via Brookston Beer Bulletin
You can thank the National Minimum Drinking Age Act of 1984 for this one. So while it's largely up to each state to decide their legal drinking age, this law told these states that they had to enact a minimum drinking age of 21 or else they would lose 10% of their highway funding. Since no state wanted to give up that funding, that means that no one under the age of 21 can legally purchase or publicly possess alcohol.

6. What's the difference between "&" and "and" in movie credits?

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via Movies
The ampersand (&) means that two writers worked together to write the script, whereas "and" means that one writer re-wrote the others' work.

7. Why can't we decide if tomatoes are fruits or vegetables?

15 Answers To Things You've Always Wondered About 18
via Wikipedia
It looks like a vegetable, but it's classified as a fruit. Or is it the other way around? The tomato is technically a fruit since it protects and contains the seeds of its plant, but according to a Supreme Court ruling, is is classified as a vegetable. Why? The Tariff Act of March 3, 1883 required a tax to be paid on imported vegetables, but not fruit, and they didn't want any tomato farmers going untaxed.

8. Why do we say "cheese" when we get our pictures taken?

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via giphy
The origin is unknown, but when you say "cheese," the act of saying the word turns the corners of your mouth lift up, your cheeks lift, and you show off a toothy grin.

9. What is it about showers and creative thoughts?

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via First to Know
Our best ideas come to us in the shower because its a mindless task. Since your shower routine doesn't require much thought, it frees your mind to wander and think of something else.

10. Why is the sky blue?

15 Answers To Things You've Always Wondered About 27
via giphy
Much like our veins appear blue, it has everything to do with wavelengths and blue light. Blue light scatters more than the other colors in the spectrum because it travels as shorter, smaller waves.

11. Why do different languages call countries by different names?

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via World Maps
Most of us know Germany as, well, Germany. But to the Germans, they known their homeland as Deutschland. The simplest explanation is that languages pre-date countries, sometimes by centuries. So when small settlements joined together to create countries, like Germany, there were multiple names for the region, depending on the language. It's all in who you know.

12. Why do our fingers get wrinkly in the shower?

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via Wikipedia
Scientists have figured out why our fingers and toes get wrinkly during bathtime. It actually has nothing to do with absorbing the water, and everything to do with improving our grip on things underwater. Think of it like the treads in a tire giving a much better grip in slippery conditions. The human body is amazing.

13. Why does the letter U almost always accompany the letter Q?

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via flickriver
The reason for this pairing is because QU is a digraph, which is a pair of letters that represents a single sound. In this case, it's "kw." Basically, the two are treated as a single character in the English language, mostly from borrowed words from Latin. Q's without U's aren't as common, but can be found in words like Iraq.

14. How do magnets work?

"Magnets: how do they work?" Actually, The Insane Clown Posse asked a good question. According to Northeastern University, a magnet is simply any object that produces its own magnetic field and interacts with other magnetic field. Magnets have two poles (north and south) and the magnetic field starts and the north pole and ends at the south pole. 
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via Northeastern University
So if you have two magnets next to each other, and their north poles are facing each other, you will feel them repel. And when you place a north pole next to a south pole, they will attract. Science.

15. Why do we have eyebrows?

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via giphy
You have to pluck them and prune them, so why do they even exist? Aside from being a very distinct feature on your face that helps you communicate, there's actually a very good reason eyebrows exist. If you've ever run longer than to catch a bus, you know just how sweaty your forehead can get - sweat can even drip down into your eyes and cause temporary blindness. And that's why your eyebrows exist. Consider them a built-in headband!
Collage source: theBERRY