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Why Does Hot Water Sometimes Feel Cold?

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Home experiment time! Go run some hot water, either in a sink or tub, and stick your hand under it.

Some of you might be mad at me—the water was hot and you have no idea why I asked you to scald yourself. (We'll work through this.) Some of you, though, are going to be a little confused. You know the water was hot, but when you put your hand under it, it felt ice cold.

All together now, in your best Jerry Seinfeld voice: "What's the deal with that?"

Feeling Spots

Our hands have a mess of sensory receptors that all receive different sensations. These receptors send signals to the brain to help us make sense of what we're touching. We've got some receptors that receive sensations of cold (cold spots) and others that receive warmth (warm spots).

Neither of these temperature receptors pull double-duty. If you touch a cold spot with something hot, it's still going to do what it's supposed to do: send a cold signal. If you touch a warm spot with something cold, it's still going to tell the brain that you're touching something warm.

Mixed Signals

Neurologists call instances when these spots send the "wrong" signal in response to a stimulus paradoxical cold and paradoxical warmth. If you want to try another experiment (and you still trust me after the hot water thing), grab a pen and lightly poke the point around between your knuckles. In some spots it will feel cold, in some it will feel warm.

Of course, when you run your hand under hot water, the water touches both warm and cold spots. In cases like this, where the stimulus is strong enough, the receptors get confused and sometimes the wrong signal gets sent to the brain, even though both temperature receptors are being stimulated. Sometimes it only takes a second for things to correct themselves; sometimes it takes a few minutes.

How did the hot water experiment turn out for you?

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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 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.

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