Q. What causes hiccups?

—Jazelle G., 13, Oregon

A. Hiccups are your body’s way of making you stop eating and drinking. Ever try to eat while you're hiccupping? Not possible, says hiccupmeister George Triadafilopolous, chief of gastroenterology at the Veterans Hospital in Palo Alto, California. He has cared for many people with hiccups, including some who couldn’t stop hiccupping for days at a time.

When your stomach is full, it bloats and rubs against the big muscle that covers it like a cap (the diaphragm muscle). The rubbing triggers the “hiccup center” in your brain and there you—HIC—go. To stop the feeding frenzy, a hiccup freezes the squeezing action of the tube that moves food and drink from your mouth to your stomach.

Most often hiccups erupt because you gulp down your food or drink too quickly. When you do that, you swallow a lot of air with your food. That puffs out your stomach and—you know the rest. HIC!

—Rosanne

Q. Although the tops of mountains are nearer to the sun than lowlands, why do mountains feel colder?

—Dawn C.

A. “It feels colder on mountaintops because it usually is,” Stephen Schneider, a climatologist (climate expert) at Stanford University, told me. When the sun’s energy reaches Earth, he explained, most of it goes into warming the rock, soil, and water on our planet’s surface, which then warms us. So climbing a mountain is like walking away from a warm radiator—naturally, you get cooler. Two other things also play a part, he said, but getting close to the sun isn’t one of them. The top of the highest mountain is less than seven miles high. That’s less than one ten-millionth of the way to the sun—not enough to make a difference.

—Robert

Q. Who was the first person to eat popcorn at the movies?

L. L.W. U. (Lost Letter; Write Us)

A. Historians don't know who it was or where it happened, but they do know that popcorn burst into cinemas throughout North America about 1929 or 1930. By that time, in fact, movies were among the few places that didn't sell popcorn.

I got the whole salty story from Andrew Smith, who teaches the history of food at the New School University in New York City. Smith's book Popped Culture: A Social History of Popcorn is a gold mine of popcorn-related facts. People had been peddling popcorn on the streets and at ballgames in the United States since the 1840s, he says, and when movies came along in 1889, vendors were naturally eager to sell popcorn there, too. Early movie-house owners, however, wanted nothing to do with the stuff. Their theaters were elegant places, with expensive carpets and gleaming chandeliers. Spilled popcorn and greasy smoke from popcorn poppers wouldn't fit in, they thought. But a stock- market crash in 1929 and the Great Depression that followed it made millions of people poor almost overnight. To keep them buying tickets, cinemas across the United States scrambled to change their exclusive image and added some extras, including popcorn.

—Robert

Nobody is perfect. Sometimes, your intrepid Q&A columnists track down an answer only to find that the name of the questioner has fallen into the Fan Mail Pit. If you recognize your long-lost question here, let us know, and we'll re-attach your name to it at last.

—Robert

Q. What's the difference between sand, soil, dirt, and all those other things?

—Eli, 7, Northampton, Massachusetts

A. Soil scientist Randy Southard of the University of California, Davis, told me that the main difference is that soil is way more interesting than all those other things, because soil always contains stuff that's alive. Most states even have a "state soil," he pointed out. Yours is the Paxton series, which covers 7.5 percent of Massachusetts. It formed from rocks dropped by glaciers as they crept over the state during the last Ice Age.

— Rosanne

My whole answer to this question was too long to fit onto the page of the magazine. Here's what got left out:

Glossary of dirt-like things:

Sand: Any kind of mineral particles that are between 50 to 2000 microns across. In other words, they're all about the size of a grain of SAND.

Soil: Interesting dirt. It's the combination of mineral particles, roots, bacteria, viruses, and dead plants and animals that develops in one place after years of weathering and rotting.

Dirt: Even soil scientists sometimes use the word "dirt" when what they mean is soil. Really, though, dirt is a more general term for the natural materials that the ground is made of—as long as it's soft enough stuff to dig into. If not, it's probably a rock.

Mud: Wet dirt.

Crud: Disgusting dirt.

Quicksand: Very mushy wet sand. It lurks on riverbanks and beaches and near underground springs.

— Rosanne

Q. Why do the chocolate chips in chocolate chip cookies stay soft and melty even when the cookie is not warm anymore? Why doesn't the chocolate solidify again?

—Lucia R., 12, Ohio

A. Melting wrecks the network of tiny crystals that gives chocolate that snap you get when you bite into a fresh-out-of-the-bag chocolate chip. Once the network disintegrates, the chips stay soft even though they're not warm anymore.

It's kind of sad, since chocolate makers go to so much effort to give chips their crunch. First they melt the chocolate. Then they carefully stir and cool it to create cocoa butter crystals with a uniform shape. These crystals fit together to form a hard, stable network. Once the crystals form the network, chocolate makers say the chocolate is "tempered." Then we come along, bake the chips in our cookies, and mess the crystals all up.

Peter Greweling, a professor of baking and pastry at the Culinary Institute of America, says the crystals in tempered chocolate all look like 3D asterisks. The crystals in soft chocolate have lots of different shapes and don't fit together nearly as well. But that's not the end of the story. Peter tells me that the chips in a chocolate chip cookie will eventually harden up again—if the cookie survives long enough. "After a few days, the unstable crystal forms mutate up to more stable ones. The chips get a little harder and start looking grayish. They taste good that way, too."

—Rosanne

Q. Is there a chemical in nail polish that shortens your life by one second for every coat?

—L. L.W. U. (Lost Letter; Write Us)

A. Chemicals don't affect people that precisely, but ingredients in some nail polishes are causing concern. The main one is a chemical called dibutyl phthalate, or DBP, which makes the polish spread and dry more evenly. Some scientists are worried because DBP and similar chemicals have been found in human blood and because they cause birth defects and other health problems when scientists feed big doses of them to mice. But companies that make chemicals and nail polish say that force-feeding DBP to mice is very different from dabbing it on your fingernails. Unfortunately, nobody really knows how much DBP does get into your body through your nails or how much it takes to harm a person. Until scientists find out, you can expect to hear a lot more about what chemicals in nail polish might be doing to you.

—Robert

Q. Why are mice so commonly used in experiments done by scientists? I have to do a project for school, and I want to find out if mice can memorize the correct path to get out of a maze. Could I use hamsters instead, or are mice better?

— Pablo R., Florida

A. I sent your question to two psychology professors at the University of Toronto, Canada, who have done many experiments to find out how mice and other rodents learn. The problem with hamsters, Robert McDonald says, is that their memory gets better and worse at different times of day. For a good, solid round-the-clock learner, he says, the pros use black-and-white Long-Evans rats. His colleague Sarah Shettleworth, however, says a hamster should have no problem learning a maze. Just attach the maze to the hamster's home cage and put a pile of sunflower seeds at the far end of the maze. The hamster will go into the maze when it gets hungry and will quickly find its way to the seeds and back.

As for why you see more rats and mice than hamsters in the lab, Shettleworth says a lot of it is just tradition. "The very first maze-learning experiments were done with rats over a hundred years ago, before hamsters were even known as pets in North America, let alone laboratory animals," she says. "Mice then began to be used because they are smaller and even easier to keep and breed in the laboratory."

—Robert

Q. In the January [2003] Muse you said that hiccups stop you from eating. My problem is this: I almost always get hiccups when I haven't eaten in a long time. Never when I have eaten too much. Why is that?

—Abbey, I 3

A. I e-mailed Abbey's question to hiccup expert George Triadafilopoulos. He said that you get hiccups because your diaphragm, the muscular sheet that lies above your stomach, gets irritated. This can happen when you've overeaten—or when you've swallowed air. Sometimes people who have not eaten for a while have a lot of air in their stomachs, and this may be what is causing Abbey's hiccups.

—Rosanne

Q. Why does Swiss cheese have holes in it?

— Dana M., Washington

A. Bacteria blow the bubbles we see in Swiss cheese. Like all kinds of cheese, Swiss starts off as milk with bacteria mixed in. Among the three types of bacteria used to make it is one type, Propionibacter shermani, that produces carbon dioxide gas. Because the cheeses outer rind holds the gas in, it builds up and forms bubbles.

The bacteria are also the secret of the "Swiss" taste that sets Swiss cheese apart from other kinds. Its the yummy taste of propionic acid.

Getting these bacteria to behave takes a lot of skill. As a result, Swiss cheese is one of the hardest cheeses to make. As they say in Switzerland: "Anyone can make the holes, but only the Swiss can make the cheese."

—Rosanne

Q. Why do your feet fall asleep?

—Madeleine O., Alaska

A. That weird feeling is your foot saying: AAAACK, I'm getting strangled. The nerves in your complaining foot are desperate for supplies, mainly oxygen and sugar, probably because you're sitting in a position that cuts off blood flow. Or it could be that the nerves themselves are getting squeezed. In either case, the result is that some of the many nerve cells in your foot stop sending any messages while others start shooting off like crazy. Your brain interprets these mixed signals as a tingling feeling.

Moving your foot is a good idea because squeezing your nerves or arteries for too long—like for more than a few hours—can damage them. So if your foot is asleep, wake it up!

—Rosanne

Q. Do insects catch colds?

—Emily F.

Insects don’t catch colds. The major reason for this is their lack of noses. No nose, no cold. Simple as that.

But what if insects did have noses? “They would probably get the sniffles,” insect virus expert Hanna Walukiewicz* told me. But a sniffly bug’s problems would go waaay beyond a runny nose. That’s because colds are usually caused by a virus (a rhinovirus, usually), and insects can’t fight viruses the way people and other vertebrates can.

“Since insects lack an immune system that can fight the virus, the rhinovirus would grow uncontrollably and would probably result in paralysis,” Hanna said. Yes, she said paralysis. “That’s what happens to insects when they get infected by close relatives of the rhinovirus.”

Yikes. I’ll take a cold over acute bee-paralysis virus or aphid lethal-paralysis virus any day.

—Rosanne

*Hanna Walukiewics studies insect viruses at the Scripps Research Institute in La Jolla, California.

Q. How many vocal cords do dogs have? How many vocal cords do cats have?

—Mallory & Bryn, Massachusetts

A. Dogs have two vocal cords and cats have two, too. Air flowing up from their lungs vibrates their vocal cords and creates woofs and growls, meows and yowls.

But to purr, cats do a vocal-cord trick that’s impossible for dogs and most other animals. “Cat purring is made by very rapidly tensing and contracting the muscles inside the vocal cords,” says W. Tecumseh Fitch,* a scientist who studies vocal cords and the sounds they make.

Most cat species can purr, but not all. “Lions, tigers, jaguars, and other big cats cannot purr, probably because they have huge enlarged vocal cords to allow them to roar,” he says.

—Rosanne

*W. Tecumseh Fitch III teaches animal behavior and the evolution of language at Harvard University.

If you know anybody with a cooler name than W. Tecumseh Fitch III, I'd like to hear about it. —Robert

Q. Why do older people get sick less often than younger people?

—Nasiha M., age 13

A. I e-mailed your question to Esther Sternberg, a doctor who is in charge of research into the brain and the immune system at the National Institute of Mental Health in Washington, D. C. Here's what she wrote back:

"In some cases older people get sick less often and in others they get sick more often. One reason they might get sick less often is that after getting lots of different flus and colds in childhood, they develop antibodies to those germs, just like the antibodies your white blood cells make when the doctor gives you a vaccination. The next time the person is exposed to a germ, those white blood cells can fight the illness more quickly. Sometimes, though, as people age, their immune systems weaken and become less able to fight infection, and so they will be more prone to getting sick when they are exposed to a flu or cold virus. This happens especially if the person is under stress, is not eating well, or has some other illness."

—Robert

Q. What was the first video game?

—Patrick N., age 8-1/2

A. The first video game was "Tennis for Two," designed in1958 for visitors day at Brookhaven, an atomic energy research lab in New York. The game's inventor, William Higinbotham, came up with it to show off what his group could do.

I got a look at the game by watching a video on the lab's Web site. The game had a round black-and-white screen that was just five inches across. It gave players a side view of a tennis court with a blip symbolizing the ball. Each player had a metal control box mounted with a knob to adjust the ball's angle and a button to give it a thwack. If the ball hit the net, it bounced back.

Very low-tech, but it must have been fun. People lined up to play by the hundreds on visitors day 1958 and 1959.

—Rosanne

Q. Why is fruit usually green before it ripens?

—Michelle, age 9

A. There are several reasons, all tied together.

I sent your question to Gilbert Muth*, a biologist, and Beth Mitcham*, a fruit researcher. Unripe fruit, they told me, contains two kinds of green chemicals: acids, which also make the fruit sour, and chlorophyll, the same chemical that leaves use to capture energy from sunlight. Green fruit makes energy just as green leaves do. When it ripens, though, the fruit stops doing that. Then the chlorophyll disappears, letting other colors show through. At the same time, chemical reactions start turning the sour acids into sweet sugars, another process that takes away the green. Other reactions break down some of the fruit's cells, making hard fruit soften and start to give off a fruity smell.

Those changes are all connected, Mitcham says. They help a fruit do its job: getting eaten, so the birds and animals doing the munching will spread the seeds inside it far and wide. The softness and sweetness make it nicer to eat, and the changes in color and odor signal that the fruit is ready.

—Robert

*Gilbert Muth is a biologist at Pacific Union College in California. Beth Mitcham is a pomologist (fruit researcher) at the University of California, Davis.

Q. Why doesn't glue stick to the inside of the glue bottle?

—Zac B., Washington

A. The bottle keeps the glue inside from drying out. Wet glue doesn't have much holding power. That's why it won't stick inside the bottle, chemist Greg Ferguson* told me.

Ferguson gave me the inside scoop on glue: Most glues are made of long stringy molecules that react to air by shedding a water molecule. But the reaction is a two-way street. So inside your glue bottle the loose water molecules latch right back on and the glue stays wet.

Unless, of course, you forget to put the lid on tight. Then the water escapes, and you—and your glue—are stuck.

—Rosanne

*Greg Ferguson is a professor at Lehigh University in Bethlehem, Pennsylvania, where he studies and teaches surface chemistry.

copyright © 2003 Robert Coontz and Rosanne Spector