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How Do Cats Purr?

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Biologists used to think that purrs were the sound of blood surging through cats’ inferior vena cava, the large vein that carries blood from the lower half of the body into the heart. More recent research suggests that the sound is actually produced by laryngeal muscles, which are responsible for moving the vocal cords and opening and closing the glottis (space between the cords).

Signaled by a “neural oscillator” in the cat’s brain, the muscles rhythmically contract and rapidly open and close the glottis. As the cat breathes in and out, air hits the vibrating muscles and the glottis, producing bursts of noise 25 times a second, which gives us the familiar purring sound. The signal from the central nervous system that sets the whole thing in motion doesn’t appear to be controlled by the cat, making a purr more of a muscular twitch than a conscious vocalization.

Cat Got Your Hyoid Bone?

The mechanism for purring seems simple enough, so it's puzzling that not all cats can make the sound. Scientists used to think that only domestic cats could purr, but gradually found that other members of the Felinae subfamily, like bobcats, cheetahs, lynxes, pumas and others, could also do it. Their cousins in the subfamily Pantherinae, like lions, leopards, jaguars and tigers, meanwhile, don’t seem to be able to purr. The hyoid bone, which sits in the throat and provides support for the tongue and larynx, might make the difference. While purring cats tend to have rigid hyoid bones, the bigger cats have more flexible, less bony hyoids that let them roar but may keep them from purring.

It might be more complicated than that, though. The extra pads of tissue that give big cats' roars a little oomph could make it more difficult or impossible for them to purr. Some might have the ability to purr, but simply don’t, or haven’t been heard doing it. Some big cats have even been known make purr-like noises, but only when exhaling, while smaller cats can purr throughout the breathing cycle. These purr-like sounds have yet to be acoustically analyzed to see if they’re true purrs or not.

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

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

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

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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