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Why Do I Sometimes Scratch One Body Part and Feel It on Another?

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Ever scratch an itch on your stomach and feel the scratch on your elbow? Or scratch your leg and feel a prickly sensation on your neck? You’re not alone. Lots of people report feeling a sensation from a scratch in places far from where they’re scratching, including scratches on the ear that produce tickles in the throat and mixed signals between their thumb and their tongue. 

It’s one of those delightfully weird things your body does, and it’s been studied, albeit infrequently, for hundreds of years. English clergyman/scientist Stephen Hales first described the phenomenon in the 1730s, referring to it as “instances of the sympathy of the nerves.” About a century later, physiologist Johannes Muller came along and applied one of those cool words to it that the Germans are really good at coming up with: mitempfindungen. Since then, we’ve just called it “referred itch” in English. 

For most people, referred itch is just a weird annoyance. It doesn’t do any damage or have any ill effects, and so it doesn’t get a whole lot of research attention. Scientists haven’t even been able to nail down how common it is. One study found that it only happens in 10 percent of the population. Another said 20 percent. Still others put the figure at anywhere between half and ninety percent of people. 

How and why it happens is anybody’s guess, but scientists have a handful of hypotheses to explain what’s going on. One idea is that referred itch is the product of our complex system of nerves being “rather irregularly distributed” throughout the body. British physician Phillip Evans wrote in the 1970s that it was difficult for him to envision “such a diffuse system providing sensations that are so clearly imagined to be in small and easily localised areas of skin.” In other words, in our haphazard map of nerves, some sensations are bound to be confused. 

Another explanation in a similar vein is that some branches of a nerve may travel out in a much different path than the others and wind up in some far-flung part of the body. Again, the nervous system gets a little confused and a “stimulus at the end of one branch is interpreted as coming from a point of ending of the other.”  

It could also be that the mix up isn’t in the nerves, but the brain. In the parts of the brain that deal with our sense of touch, regions that receive and process information from different parts of the body overlap. “Hand and shoulder areas … overlap the trunk area, and the area for the thumb overlaps that for the upper part of the tongue,” Evans wrote. “There is so much overlapping that it is difficult to see how referred itches arising from different parts of the body can be coherently separated in the cortex.” 

Finally, for some people, chronic referred itches could happen in parts of the body “rendered abnormal by damage to the nervous system.”

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Big Questions
What's the Difference Between Gophers and Groundhogs?
Gopher or groundhog? (If you chose gopher, you're correct.)
Gopher or groundhog? (If you chose gopher, you're correct.)
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Gophers and groundhogs. Groundhogs and gophers. They're both deceptively cuddly woodland rodents that scurry through underground tunnels and chow down on plants. But whether you're a nature nerd, a Golden Gophers football fan, or planning a pre-spring trip to Punxsutawney, Pennsylvania, you might want to know the difference between groundhogs and gophers.

Despite their similar appearances and burrowing habits, groundhogs and gophers don't have a whole lot in common—they don't even belong to the same family. For example, gophers belong to the family Geomyidae, a group that includes pocket gophers (sometimes referred to as "true" gophers), kangaroo rats, and pocket mice.

Groundhogs, meanwhile, are members of the Sciuridae (meaning shadow-tail) family and belong to the genus Marmota. Marmots are diurnal ground squirrels, Daniel Blumstein, a UCLA biologist and marmot expert, tells Mental Floss. "There are 15 species of marmot, and groundhogs are one of them," he explains.

Science aside, there are plenty of other visible differences between the two animals. Gophers, for example, have hairless tails, protruding yellow or brownish teeth, and fur-lined cheek pockets for storing food—all traits that make them different from groundhogs. The feet of gophers are often pink, while groundhogs have brown or black feet. And while the tiny gopher tends to weigh around two or so pounds, groundhogs can grow to around 13 pounds.

While both types of rodent eat mostly vegetation, gophers prefer roots and tubers (much to the dismay of gardeners trying to plant new specimens), while groundhogs like vegetation and fruits. This means that the former animals rarely emerge from their burrows, while the latter are more commonly seen out and about.

Groundhogs "have burrows underground they use for safety, and they hibernate in their burrows," Blumstein says. "They're active during the day above ground, eating a variety of plants and running back to their burrows to safety. If it's too hot, they'll go back into their burrow. If the weather gets crappy, they'll go back into their burrow during the day as well."

But that doesn't necessarily mean that gophers are the more reclusive of the two, as groundhogs famously hibernate during the winter. Gophers, on the other hand, remain active—and wreck lawns—year-round.

"What's really interesting is if you go to a place where there's gophers, in the spring, what you'll see are what is called eskers," or winding mounds of soil, Blumstein says [PDF]. "Basically, they dig all winter long through the earth, but then they tunnel through snow, and they leave dirt in these snow tunnels."

If all this rodent talk has you now thinking about woodchucks and other woodland creatures, know that groundhogs have plenty of nicknames, including "whistle-pig" and "woodchuck," while the only nicknames for gophers appear to be bitter monikers coined by Wisconsin Badgers fans.

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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Big Questions
Why Does Santa Claus Give Coal to Bad Kids?
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The tradition of giving misbehaving children lumps of fossil fuel predates the Santa we know, and is also associated with St. Nicholas, Sinterklaas, and Italy’s La Befana. Though there doesn't seem to be one specific legend or history about any of these figures that gives a concrete reason for doling out coal specifically, the common thread between all of them seems to be convenience.

Santa and La Befana both get into people’s homes via the fireplace chimney and leave gifts in stockings hung from the mantel. Sinterklaas’s controversial assistant, Black Pete, also comes down the chimney and places gifts in shoes left out near the fireplace. St. Nick used to come in the window, and then switched to the chimney when they became common in Europe. Like Sinterklaas, his presents are traditionally slipped into shoes sitting by the fire.

So, let’s step into the speculation zone: All of these characters are tied to the fireplace. When filling the stockings or the shoes, the holiday gift givers sometimes run into a kid who doesn’t deserve a present. So to send a message and encourage better behavior next year, they leave something less desirable than the usual toys, money, or candy—and the fireplace would seem to make an easy and obvious source of non-presents. All the individual would need to do is reach down into the fireplace and grab a lump of coal. (While many people think of fireplaces burning wood logs, coal-fired ones were very common during the 19th and early 20th centuries, which is when the American Santa mythos was being established.)

That said, with the exception of Santa, none of these characters limits himself to coal when it comes to bad kids. They’ve also been said to leave bundles of twigs, bags of salt, garlic, and onions, which suggests that they’re less reluctant than Santa to haul their bad kid gifts around all night in addition to the good presents.

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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