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Outside magazine, February 2000
By Jim Collins

I've heard that snakes have hip bones. Is this for real?

J. Wilson, Washington, D.C.

Consider this an evolutionary candidate for the Weird-but-True File: No snake alive today can swivel its hips, but a few tropical species do sport remnant hip bones left over from at least 100 million years ago, back when they were lizards. As reptiles evolved into longer and slinkier snakes (a more favorable shape for slipping into narrow crevices to hunt prey and dodge predators), these proto-snakes lost their spindly legs, and somewhere along the way, their narrow hip bones. That is, except for a handful of more primitive serpents such as boas and pythons, whose vestigial femurs protrude from their scaly underbellies like stunted pincers. These comma-shaped bone spurs—about an eighth of an inch long and almost as thick as a toothpick, but not quite as sharp—still fulfill certain functions. Green tree pythons from New Guinea rely on these spurs to inflict small puncture woundson rivals. And male boas use them to caress members of the opposite sex during mating. "I hesitate to use the word 'tickle,'" says Harry Greene, a leading herpetologist at Cornell University. "But whatever it does to females sure does seem to stimulate them."

Why does frost look like lace?

Steven Riley, Vancouver, Canada

You could just as easily ask why snowflakes look like lace. Frost and snow are both frozen water crystals, and the laciness of each comes from the same two qualities: six-fold symmetry and an intricate branching pattern. When the temperature drops below freezing, water molecules arrange themselves into an expanding framework through hydrogen bonding. Thanks to the molecules' internal structure, this process occurs along six distinct axes, creating the familiar hexagonal snowflake pattern. In frost formed from dew in the air (on grass, for example), branching occurs along straight lines, resulting in a wispy layer of crystals with a distinctly lace-like appearance. But in frost formed from surface water vapor (e.g., on the inside of a tent), the crystals' patterns are curved by the surface, creating an irregular, wavy motif that certain frost experts insist looks like something else entirely. "I don't know about lace," shrugs Charles Knight of the National Center for Atmospheric Research. "It looks more like ferns to me."

How can you tell which way is north on an overcast day?

J. Shaw, New York, New York

On nautical charts, a phrase often appears alongside changeable shoals or glaciers: "Beyond this point, must rely on local knowledge." The same might be said about navigating northward. The classic rule of thumb—moss grows on the north side of trees, where conditions are shady and damp—doesn't always help. On the soggy Olympic Peninsula, for example, moss blankets every side of every tree, and only the most observant among us would be able to notice that the clumps on the north side are thicker and darker than those on the south. The upshot? "A competent outdoorsman should be aware of local patterns while the sun is shining," advises John Gookin of the National Outdoor Leadership School, "so he'll be able to recognize them in any kind of weather." Some such handy clues: In northern sections of the eastern United States, from Minnesota to Maine, fair-weather wind often comes out of the northwest; in exposed areas, tree branches typically grow with the prevailing wind, so if you know its usual direction, you can deduce north; and snowpacks are shallower on southern faces. The most obvious solutions: Familiarize yourself with your local topography—and carry a compass.

What causes that achy-chest feeling when you exercise in extremely cold weather?

A. Garcia, Madison, Wisconsin

You'd think the pain was caused by bone-chilling air hitting your lungs, but it's actually your bronchial tubes that take the hit. When you inhale, air travels from your mouth or nose into the pharynx in the back of your throat and down into these narrow airways. On bitter days the air is still cool when it gets there, shocking the surrounding muscles and causing them to spasm and contract—which in turn causes the bronchial tubes to shrink. It's this so-called bronchial constriction that creates the tight, prickly sensation in your chest, and aerobic exercise only compounds the problem. "When you're working hard," explains Murray Hamlet, director of research at the U.S. Army's Research Institute of Environmental Medicine, "you become a mouth breather, and the air has less time to warm up because it doesn't move through the nasal passage. Plus, you're increasing the volume and velocity of the air slamming into the back of your throat."Fortunately, unless you're asthmatic, the condition isn't life-threatening, and Hamlet's Rx is fairly intuitive: Tie a scarf around your mouth to warm the air, and while you're at it, get in shape. You'll gulp less chilly air and breathe more easily all around.  

Illustrations: Brian Rea

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