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Why Does Mint Make Your Mouth Feel Cold?

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Reader Lisa from Anderson, California, wrote in with a question: "Chew a piece of mint gum and then drink something. It seems colder. Why is that?"

Mint gum or candy might make everything in your mouth feel sub-zero, but like the hot water that sometimes feels cold I wrote about in 2008, the feeling is just a thermal illusion that happens when our sensory receptors get fooled by stimuli.


At the heart of the minty matter is a protein called the transient receptor potential cation channel subfamily M member 8 (TRPM8), which is expressed in sensory neurons. TRPM8 is an ion channel, a type of protein that regulates the movement of ions across the membranes of cells. Just like only certain keys can open a lock on a door, only certain stimulants can open the ion channel and access the cell. TRPM8 opens in the presence of cold temperatures and allows Na+ and Ca2+ ions to enter the cell. This changes the electrical charge within the neuron and the information being sent from the neuron to the central nervous system, eventually leading to the perception of cold.

TRPM8 doesn't just respond to cold temperatures, though.

It also activates in the presence of menthol, a waxy, crystalline organic compound found in peppermint and other mint oils. (It responds to other "cooling agents," too, like eucalyptol and icilin. Why, exactly, is unknown; menthol just happens to fit the cellular "lock.") In the presence of menthol, TRPM8 ion channels open up the same way they would if the ambient temperature in your mouth dropped. The same "hey it's cold in here!" signal is sent to the brain, even though menthol doesn't actually cause the temperature in the mouth to change. And just like that, the wondrous human brain is tricked by a piece of Doublemint.

Even after you spit the gum out, a little menthol will remain and the sensory neurons will stay sensitized. Drinking anything cold or even taking in a big breath of cool air will cause the neurons to fire again, and the double whammy of the cool temperature and the menthol will make your mouth seem extra cold. Even a hot drink will seem weirdly cool and refreshing.


TRP-V1, another ion channel on the sensory neurons, displays a similar quirk. TRP-V1 is activated by hotter temperature, but also responds to capsaicin, the chemical responsible for the spiciness of hot peppers. This can cause even ice cold drinks to feel hot.

So what would happen if you ate a chili pepper that's been in the freezer, or a warmed up mint? Or ate a hot pepper and a cool mint at the same time? Would the hot and cold perceptions cancel each other out? To be honest, we're not sure. Has anyone ever tried this at home?

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Opening Ceremony
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These $425 Jeans Can Turn Into Jorts
May 19, 2017
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Opening Ceremony

Modular clothing used to consist of something simple, like a reversible jacket. Today, it’s a $425 pair of detachable jeans.

Apparel retailer Opening Ceremony recently debuted a pair of “2 in 1 Y/Project” trousers that look fairly peculiar. The legs are held to the crotch by a pair of loops, creating a disjointed C-3PO effect. Undo the loops and you can now remove the legs entirely, leaving a pair of jean shorts in their wake. The result goes from this:

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Opening Ceremony

To this:

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Opening Ceremony

The company also offers a slightly different cut with button tabs in black for $460. If these aren’t audacious enough for you, the Y/Project line includes jumpsuits with removable legs and garter-equipped jeans.

[h/t Mashable]

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