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Chloe Effron

Why Do Some Farts Stink and Some Farts Don't?

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Chloe Effron

Kids ask a lot of questions. mental_floss has answers. WHY?, our new series for kids and parents, tackles all types of questions children have about how the world works by providing science-based, kid-friendly content. Our answers are written with early readers (ages 4 to 7) in mind, but we think they're interesting—and educational—for everyone.

Have a question? Send it to why@mentalfloss.com.

Everyone farts, every day. But not all farts are the same. Some farts make no sound but are really stinky. Others are loud but don't smell. Some you can smell clear across the room, but others you can let out without anyone noticing. (Secret: I’m farting right now!)

The smell of your booty bomb depends on what you’ve been eating. Broccoli, cabbage, onions, eggs, and meat all contain a lot of sulfur, a chemical that helps give rotten eggs their stink. When your body digests, or breaks down, those foods, the teeny-tiny creatures in your gut called bacteria feast upon the proteins in the food that contain sulfur. This process creates smelly gases like methanethiol (METH-ain-THIGH-all). When those gases leave your body, they end up as pungent farts.

All smells are chemicals in the air that your nose can pick up. Farts are made up of chemicals like oxygen, nitrogen, hydrogen, methane, carbon, and the super villain of stinkiness: sulfur. (Sulfur is the reason that skunk spray smells so gross!) The more sulfur in your toots, the more likely they are to clear the room. You also swallow air as you eat or talk. Some of that comes out of your rear end too.

Let's talk about bacteria again. When you eat carbohydrates (CARB-oh-HIGH-drates) like potatoes, bread, and vegetables, your stomach doesn’t fully digest them. They pass into the small intestine and then the large intestine, which are really long tubes leading to your anus (where poop and farts come out). Bacteria break the carbohydrates into smaller pieces. That releases gases like hydrogen and carbon dioxide. Those gases don’t smell. But other bacteria in the gut take those odorless chemicals and make them into compounds (mixes of chemicals) that do smell. Hydrogen sulfide (HIGH-dro-jen SULL-fide) is the smelliest of the gases that might come out of your butt.

For more fart science, check out AsapSCIENCE’s illustrated video explanation of why your farts don’t smell as bad as other people’s do. 


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Animals
Why Do Female Spotted Hyenas Give Birth Through Their Pseudo-Penises?
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YouTube

At the zoo, you can sometimes tell the difference between male and female animals by noting their physical size, their behavior, and yes, their nether regions. Hyenas, however, flip the script: Not only are lady spotted hyenas bigger and meaner than their male counterparts, ruling the pack with an iron paw, they also sport what appear to be penises—shaft, scrotum, and all.

"Appear" is the key word here: These 7-inch-long phalluses don't produce sperm, so they're technically really long clitorises in disguise. But why do female hyenas have them? And do they actually have to (gulp) give birth through them? Wouldn't that hurt … a lot?

The short answers to these questions are, respectively, "We don't know," "Yes," and "OW." Longer answers can be found in this MinuteEarth video, which provides the full lowdown on hyena sex. Don't say we didn't warn you.

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science
Are Sex, Drugs, and Rock 'n' Roll Really Linked? Researchers Investigate
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Around the world, sex, drugs, and rock 'n' roll are said to go hand-in-hand. But do they? As PsyPost reports, a pair of Pennsylvania psychologists recently dove into the empirical evidence tying the three together, asking college students to talk about their drug use, sex lives, and music preferences and talents to suss out whether people who play and enjoy rock music really do have more active sex lives and drug use.

Published in the journal Human Ethnology Bulletin, the study [PDF] of 467 students relied on self-reporting, which isn't typically the most reliable evidence—people are wont to exaggerate how often they've had sex, for instance—but the survey also asked them about their desires, posing questions like "If you could, how frequently would you have sex?" It also asked about how often the students drank and what drugs they had tried in their lifetimes. They also described their musical experience and what kind of music they listened to.

The results were mixed, but the researchers identified a relationship between liking faster, "harder" music and having more sex and doing more drugs. Acoustic indie rock aficionados weren't getting quite as wild as heavy metal fans. High-tempo-music lovers were more likely to have taken hallucinogenic drugs like LSD, for example, and tended to have had more sexual partners in the previous year than people who favored slower types of music. According to the study, previous research has found that attention-seeking people are more likely to enjoy "hard" music.

The study didn't have a diverse enough group either in age or in ethnicity to really begin to make sweeping generalizations about humans, especially since college students (the participants were between 18 and 25) tend to engage in more risky behaviors in general. But this could lay the groundwork for future research into the topic. Until then, it might be more accurate to change the phrase to "sex, drugs, and heavy metal."

[h/t PsyPost]

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