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Why Does the Airplane Oxygen Mask Have a Bag That “May Not Inflate”?

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If you’ve seen the airplane safety demonstration enough times, you know the drill for the oxygen masks. If there is a loss in cabin pressure the masks come down. First, you put yours over your face and pull the strap over your head, and then you help anyone else who needs it. Makes sense. You’re no good to others if you’ve passed out from lack of oxygen. But what about the next part, when they tell you that “although the bag on the oxygen mask may not inflate, oxygen is flowing to the mask”? If the bag doesn’t do anything important, why is it there?

The passenger airplane masks are “continuous flow” masks, which are different from “diluter demand” masks, which are what the crew have. A diluter demand mask only releases oxygen when the user inhales. This prevents waste of oxygen and allows the instruments on the mask to determine the exact oxygen level being delivered. It functions to make sure the crew stays alert enough to get the aircraft down into more oxygenated air.

A continuous flow mask is constantly releasing oxygen whether the user is inhaling or not. Passenger masks don’t have to function as efficiently because they’re there just to make sure you stay alive. Even with some waste, there's enough oxygen to sustain everyone until the airplane reaches denser air.

The bag on the mask allows for a bit of oxygen savings. If the mask is situated well on your face, the oxygen continuously coming out will collect in the bag as you are exhaling instead of seeping out the sides of the mask. (The air-flow on any oxygen mask is one-way. Exhaled breath does not travel back into the tube, but out of valves on the mask.) However, even if there is a good seal, if you are breathing fast (which is probably what’s going to happen in a panicky situation), you’ll probably suck down what’s going through the bag before it fills. They don't want people thinking, "Hey this thing's not doing anything!" and taking off the mask or freaking out if their neighbor's bag inflates but theirs doesn't. That’s why the safety demonstration wants to reassure you that, yes, your mask is still doing its job even if the bag isn’t inflating. You’ve got enough to worry about if the oxygen masks are down. Your oxygen mask bag shouldn’t be one of them.

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Big Questions
What Are Curlers Yelling About?
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WANG ZHAO/AFP/Getty Images

Curling is a sport that prides itself on civility—in fact, one of its key tenets is known as the “Spirit of Curling,” a term that illustrates the respect that the athletes have for both their own teammates and their opponents. But if you’re one of the millions of people who get absorbed by the sport once every four years, you probably noticed one quirk that is decidedly uncivilized: the yelling.

Watch any curling match and you’ll hear skips—or captains—on both sides barking and shouting as the 42-pound stone rumbles down the ice. This isn’t trash talk; it’s strategy. And, of course, curlers have their own jargon, so while their screams won’t make a whole lot of sense to the uninitiated, they could decide whether or not a team will have a spot on the podium once these Olympics are over.

For instance, when you hear a skip shouting “Whoa!” it means he or she needs their teammates to stop sweeping. Shouting “Hard!” means the others need to start sweeping faster. If that’s still not getting the job done, yelling “Hurry hard!” will likely drive the point home: pick up the intensity and sweep with downward pressure. A "Clean!" yell means put a brush on the ice but apply no pressure. This will clear the ice so the stone can glide more easily.

There's no regulation for the shouts, though—curler Erika Brown says she shouts “Right off!” and “Whoa!” to get her teammates to stop sweeping. And when it's time for the team to start sweeping, you might hear "Yes!" or "Sweep!" or "Get on it!" The actual terminology isn't as important as how the phrase is shouted. Curling is a sport predicated on feel, and it’s often the volume and urgency in the skip’s voice (and what shade of red they’re turning) that’s the most important aspect of the shouting.

If you need any more reason to make curling your favorite winter sport, once all that yelling is over and a winner is declared, it's not uncommon for both teams to go out for a round of drinks afterwards (with the winners picking up the tab, obviously). Find out how you can pick up a brush and learn the ins and outs of curling with our beginner's guide.

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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Why You Should Never Take Your Shoes Off On an Airplane
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What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

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