Tricky health questions answered

Do you feel like a fraud when your kids ask why the grass is green? (Because it contains chlorophyll—ring a bell?—a green pigment plants use to make their food.)

Behold this parental compendium of uncommon knowledge, which explains a few mysteries of the universe.

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What Causes Hiccups?

Hiccups usually occur when the stomach rubs against and irritates the diaphragm, a muscle at the bottom of the rib cage. An irritated diaphragm pulls back fast, forcing air sharply into the lungs, says Dr. Norman H. Edelman, the chief medical officer for the American Lung Association. When the air hits your voice box, you hiccup. This happens repeatedly until the irritation stops.

Why Doesn't Gum Stick to My Teeth?

You know how you tend to slip on wet floors? The same thing happens to your gum when it touches your teeth, which are wet with saliva. Also, when you chew, you produce extra saliva, which makes the inside of your mouth even more moist, says Irwin Smigel, D.D.S., the president of the American Society for Dental Aesthetics.

Why Does My Stomach Make Noise When I'm Hungry?

According to the Mayo Clinic, when you haven’t eaten for a while, your brain sends a message to your stomach to get ready for some grub. That signal jump-starts the grumbling, rumbling release of acids and other digestive juices. Just the sight or the smell of food can trigger the sounds, too.

Why Can't I Tickle Myself?

When somebody tickles you and you squirm and scream, you’re responding more to the surprise than to the sensation, says Dr. Ellen Marmur, the vice chair of cosmetic and dermatologic surgery at Mount Sinai Medical Center, in New York City. Since our brains can predict our own movements, we’re less sensitive to them.

But we’re very sensitive to unexpected touches, which is why we flail around when the Tickle Monster comes calling. Scientists believe the response might date back to our cave-dwelling ancestors, who needed to be on the alert for the skittering of bugs and rodents.

Why Do Feet Smell?

They’re covered in tons of bacteria—and when bacteria excrete waste (or, in kid terms, poop), it really stinks, says Dr. Jane Andersen,  a podiatrist in Chapel Hill, N.C. Why the feet in particular? Bacteria thrive in wet places, and our tootsies (which have a startling 250,000 sweat glands apiece) are among the body’s dampest spots.

Click for more answered questions from Real Simple.