Why Are Humans Ticklish?

iStock/andresr
iStock/andresr

Fabian van den Berg:

There are a few ideas about why humans experience ticklishness and there are also two kinds of tickling. One of them is a defense mechanism or warning sign that something moving is on you. Think parasites on your skin or ... no, don’t think about that. The fancy name for that is knismesis. This is the kind of tickling you feel when something soft brushes up against you. Usually, this type of tickling doesn’t make you laugh; It tends to give you goosebumps, and feel a bit uncomfortable.

Another aspect of tickling has to do with the specific spots that are ticklish. The fancy name for this one is gargalesis. This kind of tickling is more intense and leads to uncontrolled laughter. Gargalesis isn’t as straightforward as knismesis, and most likely serves some kind of social aspect and helps us bond.


Quora

There are specific spots that are ticklish in this latter way, and those are important for parents and children to form bonds. When we grow up those same spots are also erogenous zones, which help with mating, another social activity we engage in.

That these spots are also vulnerable areas on our bodies is probably no coincidence. Some experts think there is an aspect of tickling behavior meant to teach youngsters to protect their most vulnerable areas.

But other animals tickle, too. Our close cousin the chimpanzee tickles during play, though they make more of a panting, out-of-breath sound when they are laughing. They enjoy it, which they show by not leaving you alone afterward because they want you to keep going.

Elephants can be tickled as well, but my favorite is the rat.

A woman plays with her pet rat
iStock/Imagesbybarbara

There was a study where it was someone’s job to tickle rats (that must look amazing on your resume). The researchers in question were like, "Come tickle rats with me." Fun aside, this was serious research. It was known that rats make specific high-frequency noises when they play or have sex, noises of enjoyment (kind of like laughing). When they tickled the rats they made the same noises, indicating that the rats were enjoying being tickled, similar to the way humans do. It activates brain areas and pathways that also light up when humans experience joy (at least, the areas analogous to ours).

But a note must be made here: We are often quick to ascribe human emotions to animals, which can be dangerous. Animals like chimps and rats seem to enjoy tickling, so there’s reason to think they experience it in a positive way. But not all animals are like that—so experts aren't 100 percent sure they really like being tickled all that much. (Unfortunately, we can’t ask them.)

A tragic example of misinterpretation is the slow loris. These critters can be tickled, but they don’t like it. What humans interpret as enjoyment is actually fear, making the playful behavior in humans or primates literal torture for this cute-looking animal.

Tickling likely serves as a warning signal and training to protect ourselves. It has a secondary feature in humans, other primates, and rats it seems: to facilitate social bonding. But be careful who you tickle—not all animals experience the same enjoyment (some humans don’t like it either).

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

Why Does Hand Sanitizer Have an Expiration Date?

Hand sanitizer does expire. Here's why.
Hand sanitizer does expire. Here's why.
galitskaya/iStock via Getty Images

The coronavirus pandemic has turned hand sanitizer from something that was once idly tossed into cars and drawers into a bit of a national obsession. Shortages persist, and people are trying to make their own, often to little avail. (DIY sanitizer may not be sterile or contain the proper concentration of ingredients.)

If you do manage to get your hands on a bottle of Purell or other name-brand sanitizer, you may notice it typically has an expiration date. Can it really go “bad” and be rendered less effective?

The short answer: yes. Hand sanitizer is typically made up of at least 60 percent alcohol, which is enough to provide germicidal benefit when applied to your hands. According to Insider, that crucial percentage of alcohol can be affected over time once it begins to evaporate after the bottle has been opened. As the volume is reduced, so is the effectiveness of the solution.

Though there’s no hard rule on how long it takes a bottle of sanitizer to lose alcohol content, manufacturers usually set the expiration date three years from the time of production. (Because the product is regulated by the Food and Drug Administration, it has to have an expiration date.)

Let's assume you’ve found a bottle of old and forgotten sanitizer in your house somewhere. It expired in 2018. Should you still use it? It’s not ideal, but if you have no other options, even a reduced amount of alcohol will still have some germ-fighting effectiveness. If it’s never been opened, you’re in better shape, as more of the alcohol will have remained.

Remember that sanitizer of any potency is best left to times when soap and water isn’t available. Consider it a bridge until you’re able to get your hands under a faucet. There’s no substitution for a good scrub.

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Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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