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How Much Does a Fart Weigh?

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Flatus—the proper medical term for gas emitting from the intestines—has been examined at length in comedy, on YouTube, and in dorm rooms around the world. A fart's volume, however, is not often addressed. Farts consist primarily of nitrogen, hydrogen, carbon dioxide, oxygen, and methane. These gases have mass, which means farts could theoretically be measured for volume. But has anyone ever bothered? And if so, how?

Yes. And, gently. In 1991, gastroenterologists from the Human Gastrointestinal Physiology and Nutrition Department of the Royal Hallamshire Hospital in Sheffield, England published a paper in the trade journal Gut that attempted to quantify toot size. Their methodology was simple: take 10 volunteers, feed them 200 grams of baked beans on top of their normal diet, and measure their flatulence over a 24-hour period via rectal catheters.

Placed where the sun's ray cannot shine. MediQuip

To confirm their collection protocol was up to snuff, subjects sat in a bath with the rectal catheter inserted—the line led to a laminated gas bag—and farted. Since no bubbles were visible, they concluded the catheter was sealed.

The physicians determined that the average adult produces a median 705 milliliters of gas (nearly 24 ounces, or two soda cans’ worth) every day. Men and women passed equal amounts; farts tended to be more robust following a meal.

The farters varied widely in individual output, with a range of 476 ml to 1491 ml among the subjects during the 24 hours. The researchers noted that a singular fart, regardless of time of day, gender, or body size, was between 33 to 125 ml, with a median of 90 ml. That’s the equivalent of roughly three ounces of comedy.

According to Matthew Bechtold, M.D. a gastroenterologist and associate professor of Clinical Medicine at the University of Missouri, fart volume can be highly variable depending on both the amount of swallowed air and the matter produced by bacteria in the colon. Simple carbohydrates that are incompletely digested feed these normal bacteria, which then produce gases. “The main carbohydrate responsible for flatulence is raffinose, a sugar commonly found in cabbage and broccoli, which is poorly digested,” he says.

The study noted that volunteers on low-fiber diets reduced most of the fermentation gases expelled, lowering their fart volume to 200 ml for an entire day.

The researchers did not indicate whether any solid matter would—or should—be considered when evaluating fart mass. According to Bechtold, no fecal material typically escapes during a gas pass. “The anus does well at keeping solid material in while letting the gas out,” he says.  

The approximate size of your average fart.

With that settled, we posed another flatus-related query to Bechtold: If someone farted in cold weather with their pants down, could we visualize the fart similar to the way we see someone’s breath?

“Given the gas is contained in an environment of 98 degrees Fahrenheit just like the lungs, if gas is passed in a cold enough climate, it would likely be witnessed,” he says. “However, given that most patients are fully dressed with a barrier of pants between the anus and the outside environment, it generally goes unnoticed and diffuses rapidly in the air.”

Put another way: A fart is roughly the volume of an airport-approved travel bottle, and could be seen in cold weather if you were inclined to remove your pants in the name of science.

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Big Questions
Should You Keep Your Pets Indoors During the Solar Eclipse?
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By now, you probably know what you’ll be doing on August 21, when a total solar eclipse makes its way across the continental United States. You’ve had your safety glasses ready since January (and have confirmed that they’ll actually protect your retinas), you’ve picked out the perfect vantage point in your area for the best view, and you’ve memorized Nikon’s tips for how to take pictures of this rare celestial phenomenon. Still, it feels like you’re forgetting something … and it’s probably the thing that's been right under your nose, and sitting on your lap, the whole time: your pets.

Even if you’ve never witnessed a solar eclipse, you undoubtedly know that you’re never supposed to look directly at the sun during one. But what about your four-legged family members? Shouldn’t Fido be fitted with a pair of eclipse glasses before he heads out for his daily walk? Could Princess Kitty be in danger of having her peepers singed if she’s lounging on her favorite windowsill? While, like humans, looking directly at the sun during a solar eclipse does pose the potential of doing harm to a pet’s eyes, it’s unlikely that the thought would even occur to the little ball of fluff.

“It’s no different than any other day,” Angela Speck, co-chair of the AAS National Solar Eclipse Task Force, explained during a NASA briefing in June. “On a normal day, your pets don’t try to look at the sun and therefore don’t damage their eyes, so on this day they’re not going to do it either. It is not a concern, letting them outside. All that’s happened is we’ve blocked out the sun, it’s not more dangerous. So I think that people who have pets want to think about that. I’m not going to worry about my cat.”

Dr. Jessica Vogelsang, a veterinarian, author, and founder of pawcurious, echoed Speck’s statement, but allowed that there’s no such thing as being too cautious. “It’s hard for me to criticize such a well-meaning warning, because there’s really no harm in following the advice to keep pets inside during the eclipse,” Vogelsang told Snopes. “It’s better to be too cautious than not cautious enough. But in the interest of offering a realistic risk assessment, the likelihood of a pet ruining their eyes the same way a human would during an eclipse is much lower—not because the damage would be any less were they to stare at the sun, but because, from a behavior standpoint, dogs and cats just don’t have any interest in doing so. We tend to extrapolate a lot of things from people to pets that just doesn’t bear out, and this is one of them.

“I’ve seen lots of warnings from the astronomy community and the human medical community about the theoretical dangers of pets and eclipses, but I’m not sure if any of them really know animal behavior all that well," Vogelsang continued. "It’s not like there’s a big outcry from the wildlife community to go chase down coyotes and hawks and bears and give them goggles either. While we in the veterinary community absolutely appreciate people being concerned about their pets’ wellbeing, this is a non-issue for us.”

The bigger issue, according to several experts, would be with pets who are already sensitive to Mother Nature. "If you have the sort of pet that's normally sensitive to shifts in the weather, they might be disturbed by just the whole vibe because the temperature will drop and the sky will get dark,” Melanie Monteiro, a pet safety expert and author of The Safe-Dog Handbook: A Complete Guide to Protecting Your Pooch, Indoors and Out, told TODAY.

“If [your pets] have learned some association with it getting darker, they will show that behavior or at a minimum they get confused because the timeframe does not correspond,” Dr. Carlo Siracusa of Penn Vet Hospital told CBS Philly. “You might put the blinds down, but not exactly when the dark is coming but when it is still light.” 

While Monteiro again reasserts that, "Dogs and cats don't normally look up into the sun, so you don't need to get any special eye protection for your pets,” she says that it’s never a bad idea to take some extra precautions. So if you’re headed out to an eclipse viewing party, why not do your pets a favor and leave them at home. They won’t even know what they’re missing.

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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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