Now that it's almost summer I have to ask: What exactly is heat lightning?

—Russ Sauvageau, Ocala, Florida

Sometimes mistakenly regarded as an exotic subspecies of lightning—a bolt from Zeus's reserve quiver—heat lightning is actually just a colloquialism for any kind of atmospheric electricity that's too far away to be heard. It's lightning without thunder, in other words. On summer evenings—particularly in wide-open country that permits unobstructed vistas—heat lightning appears as the flickerings of a storm that may be as much as 100 miles away, a diffuse luminance that looks like a floodlight shining in the deepest recesses of a distant cloud. Since thunder's sound waves ordinarily can travel no more than 15 miles, heat lightning seems to be silent—a noiseless light show that can have an especially eerie beauty. Sometimes storms, like children, should be seen and not heard.

Is it true that a great fright can cause your hair to turn gray suddenly?

—Margo Stratton, Minneapolis, Minnesota

There is a large body of blanched-hair folktales out there—dubious-sounding anecdotes associated with the traumas of war, natural catastrophes, maulings by grizzlies, and other moments of intense horror. (Barbara Bush, for example, is rumored to have silvered from the shock of a daughter's sudden death.) Such stories notwithstanding, it's a woefully understudied phenomenon, and many hair biologists suspect it doesn't happen at all, at least not with the dramatic immediacy depicted in horror movies. Prevailing medical opinion suggests that, at the very least, people who claim their hair turned white "overnight" are mistaken about the time line. Experts agree that most documented cases of rapid hair-whitening can be attributed to a rare form of alopecia areata, a genetic autoimmune disease in which T cells mistake hair follicles for a foreign substance and launch an aggressive counterattack that results in partial or complete baldness. On such occasions, the immune system inexplicably targets only pigmented hairs, causing them to fall out, while gray hairs, which are often actually colorless and thus may be far more numerous than a person realizes, stay put. It's a shedding process that happens not in a single night, but over a period of weeks or months, leaving behind a patchier version of the Phil Donahue corona. How this odd self-allergy is linked to stress is still a mystery. "Emotional trauma may throw your immune system off-kilter," posits Rose Kozar of the National Alopecia Areata Foundation. "Which can trigger a predisposition for a disease that you never knew you had."

Why does my husband's wetsuit have such a horrible smell? It's unnatural!

—C. P., Houston, Texas

That rotten, eggy stink you're referring to is entirely natural. In fact, you couldn't design a better habitat for odoriferous microorganisms than a neoprene wetsuit. The rubbery material, expressly designed to be porous, is honeycombed with thousands of tiny air-filled tunnels, any one of which makes a perfect niche for colonies of microscopic critters that float around in oceans and lakes (vibrio bacteria, diatoms, and algae are usually the principal offenders). Once they attach to your wetsuit, these invaders burrow into the darkest, wettest interstices and begin feeding on keratin from your skin, salts from your sweat, fats from your body oils, and even nitrogen from your urine. In a matter of hours, a complex food chain develops, with various forms of mildew soon joining the party. The final ingredients for wetsuit fetor are prolonged darkness and heat. Leave a dripping wetsuit—one you've neglected to rinse with a neoprene-friendly disinfectant—in a sun-baked trunk for a week, and you'll not only need a new BodyGlove, you'll want a new car.

Do ostriches really bury their heads in the sand to avoid being attacked?

—Julian Holmes, Seattle, Washington

Crocodiles don't really cry. Hyenas don't laugh. And no, the world's biggest birds do not plunge their heads below ground when confronted with a difficult situation. In fact, ostriches, a species native to the semiarid grasslands of eastern Africa, are extremely jealous and scrappy micromanagers of their turf. Where, then, did this misconception come from? Ostriches do eat sand (it's grist for their gizzards), so their beaks are often caked with the stuff. And when they're resting, they tend to droop their three-foot-long necks and lay their heads on the ground. Optical illusion may also play a role: If you spot a clump of lounging ostriches from a distance, their prostrate noggins appear to be "buried" in the swimming waves of the heat shimmer. They're not avoiding you, however. As soon as the hypervigilant birds detect your presence, they'll pop their heads up and, if provoked, charge you with their muscular legs and menacing, two-toed feet. You've become their reality; they're dealing with it.

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