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How Do Countries Choose Which Side They Drive On?

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Chaos has descended this week on the tiny Pacific island of Samoa after government officials decided to force the entire nation to switch sides of the road on Monday. While Samoan officials insist there have been no accidents as a result of asking drivers to switch from driving on the right side of the road to driving on the left, many non-driving Samoans have been left stranded because the island's buses now open to the middle of the road.

Samoa is the first nation since the 1970s to switch sides and did so, they say, to end their reliance on left-hand drive vehicles imported at great expense from America. All well and good, but the real question here is why do different nations drive on different sides of the roads? Here in England, where traffic comes from the right, it took me more than a few weeks to stop looking left every time I went to cross the street—training that was completely undone when I went to France for two weeks at the end of the summer.

So what is the deal with the "wrong" side of the road? How do countries decide which side they drive on?

Because The Pope Said So

According to some sources, about a quarter of the world drives on the left, as they do in Britain. This isn't too surprising, since at one time Britain owned about a quarter of the world. Traveling on the left side of the road was a practice that started with the feudal societies of Western world, like the proto-British empire "“ back in the day, you never knew who'd you pass on the road, so best to keep your sword arm between you and them. In 1300 AD, Pope Boniface VIII codified the practice with a law that decreed that pilgrims headed for Rome should keep on the left.

The Birth of the Left-Hand Drivers' Seat

Things were going fine until the advent of market-based agriculture on a grand scale. In the 1700s, farmers in the US and France began hauling their products to market in big rigs pulled by many horses. Because these wagons typically had no place to sit, drivers would sit on the rear left horse, with their right arm free to whip the team along "“ and the left-hand drivers' seat was born. Drivers naturally tended to ride on the right side of the road now, because it was safer to meet oncoming vehicles from where you could see their wheels. In 1792, a Pennsylvania law required that vehicles keep right, other states following soon after.

Because Napoleon Said So

Another explanation blames Napoleon. Because Napoleon was left-handed, he demanded that everyone approach from the right, so he could keep his sword arm between himself and anyone he'd meet. That's not exactly true; the custom of keeping to the right actually pre-dated Napoleon, but he did make sure his troops followed it whilst they spread their Empire, and from Napoleon's lips to law. Switzerland, Germany, Italy, Poland, and Spain, which were all at one point under Napoleon's either direct control or influence, subsequently drive on the right.

It's an England/France Thing

So on two different continents, the "keep right" rule was becoming entrenched "“ while in England, keeping left remained the only way to go, especially after a 1756 city ordinance decreed that all traffic on the London Bridge must keep to the left. From there, it was all about influence.

Though not a hard and fast rule, places that were under French and US influence kept right, while those under the British Empire and its influence still kept left.

In Japan in 1859, for example, a British ambassador was able to convince the government there to keep left, a major coup for the lefties and Britain (this is what the Brits say; the Japanese, however, may disagree and claim that their decision to keep left had more to do with samurai warriors and their needs).

Because Hitler Said So

With the invention of the automobile, countries had good reason to pick a side and stick to it, although not all did. By 1938, there was another reason: Wherever Hitler invaded, he forced the native populations to drive on the right. Parts of Austria, including Vienna, Hungary and Czechoslovakia, that had historically driven on the left now had to drive on the right.

Ask Your Neighbors

Countries were still making "which side?" decisions well into the second half of the 20th century. Sweden, for example, switched to driving on the right in 1967 because by then, most of the countries their burgeoning car industry sold to were right-side countries. By this time, the clearest indicator of which side a country drives on became what its neighbors did, and with whom they traded.

Of course, some places, like the US Virgin Islands, confuse the issue even more by driving left-hand side cars on the left side of the road "“ it's the only place under US purview that does so.

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Big Questions
Why Can't Dogs Eat Chocolate?
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Even if you don’t have a dog, you probably know that they can’t eat chocolate; it’s one of the most well-known toxic substances for canines (and felines, for that matter). But just what is it about chocolate that is so toxic to dogs? Why can't dogs eat chocolate when we eat it all the time without incident?

It comes down to theobromine, a chemical in chocolate that humans can metabolize easily, but dogs cannot. “They just can’t break it down as fast as humans and so therefore, when they consume it, it can cause illness,” Mike Topper, president of the American Veterinary Medical Association, tells Mental Floss.

The toxic effects of this slow metabolization can range from a mild upset stomach to seizures, heart failure, and even death. If your dog does eat chocolate, they may get thirsty, have diarrhea, and become hyperactive and shaky. If things get really bad, that hyperactivity could turn into seizures, and they could develop an arrhythmia and have a heart attack.

While cats are even more sensitive to theobromine, they’re less likely to eat chocolate in the first place. They’re much more picky eaters, and some research has found that they can’t taste sweetness. Dogs, on the other hand, are much more likely to sit at your feet with those big, mournful eyes begging for a taste of whatever you're eating, including chocolate. (They've also been known to just swipe it off the counter when you’re not looking.)

If your dog gets a hold of your favorite candy bar, it’s best to get them to the vet within two hours. The theobromine is metabolized slowly, “therefore, if we can get it out of the stomach there will be less there to metabolize,” Topper says. Your vet might be able to induce vomiting and give your dog activated charcoal to block the absorption of the theobromine. Intravenous fluids can also help flush it out of your dog’s system before it becomes lethal.

The toxicity varies based on what kind of chocolate it is (milk chocolate has a lower dose of theobromine than dark chocolate, and baking chocolate has an especially concentrated dose), the size of your dog, and whether or not the dog has preexisting health problems, like kidney or heart issues. While any dog is going to get sick, a small, old, or unhealthy dog won't be able to handle the toxic effects as well as a large, young, healthy dog could. “A Great Dane who eats two Hershey’s kisses may not have the same [reaction] that a miniature Chihuahua that eats four Hershey’s kisses has,” Topper explains. The former might only get diarrhea, while the latter probably needs veterinary attention.

Even if you have a big dog, you shouldn’t just play it by ear, though. PetMD has a handy calculator to see just what risk levels your dog faces if he or she eats chocolate, based on the dog’s size and the amount eaten. But if your dog has already ingested chocolate, petMD shouldn’t be your go-to source. Call your vet's office, where they are already familiar with your dog’s size, age, and condition. They can give you the best advice on how toxic the dose might be and how urgent the situation is.

So if your dog eats chocolate, you’re better off paying a few hundred dollars at the vet to make your dog puke than waiting until it’s too late.

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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Big Questions
What is Duck Sauce?
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A plate of Chinese takeout with egg rolls and duck sauce
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We know that our favorite Chinese takeout is not really authentically Chinese, but more of an Americanized series of menu options very loosely derived from overseas inspiration. (Chinese citizens probably wouldn’t recognize chop suey or orange-glazed chicken, and fortune cookies are of Japanese origin.) It would also be unusual for "real" Chinese meals to be accompanied by a generous amount of sauce packets.

Here in the U.S., these condiments are a staple of Chinese takeout. But one in particular—“duck sauce”—doesn’t really offer a lot of information about itself. What exactly is it that we’re pouring over our egg rolls?

Smithsonian.com conducted a sauce-related investigation and made an interesting discovery, particularly if you’re not prone to sampling Chinese takeout when traveling cross-country. On the East Coast, duck sauce is similar to sweet-and-sour sauce, only fruitier; in New England, it’s brown, chunky, and served on tables; and on the West Coast, it’s almost unheard of.

While the name can describe different sauces, associating it with duck probably stems from the fact that the popular Chinese dish Peking duck is typically served with a soybean-based sauce. When dishes began to be imported to the States, the Americanization of the food involved creating a sweeter alternative using apricots that was dubbed duck sauce. (In New England, using applesauce and molasses was more common.)

But why isn’t it easily found on the West Coast? Many sauce companies are based in New York and were in operation after Chinese food had already gained a foothold in California. Attempts to expand didn’t go well, and so Chinese food aficionados will experience slightly different tastes depending on their geography. But regardless of where they are, or whether they're using the condiment as a dipping sauce for their egg rolls or a dressing for their duck, diners can rest assured that no ducks were harmed in the making of their duck sauce.

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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