Question: Why does someone always boil water when a woman unexpectedly goes into labor?

Answer: What most of us know about birthin' babies is what we've seen in old movies. We know that if a woman suddenly goes into labor in our little cabin on the prairie, we are supposed to "get some sheets and boil some water." After that, we close our eyes and stick our fingers in our ears and hope for the best.

The movies never explain what you are supposed to do, exactly, with the sheets and the boiling water.

There's one obvious explanation for the water, which is that you'd use it to sterilize instruments, like a knife for cutting the umbilical cord. But there are some nagging problems with that answer. For one thing, no one ever says anything about getting a knife; all the emphasis is on the water. Moreover, we are led to believe by sources that the boil-the-water tradition is centuries old, but until the late 1800s, no one knew about the spread of germs and doctors didn't realize they had to wash their hands or sterilize any equipment.

In fact, it was an obstetrician, Ignaz Semmelweis of Austria, who first understood that doctors were spreading "puerperal fever" from one mother to another as they made their rounds. Semmelweis would wash his hands with carbolic acid, and he excoriated his fellow obstetricians for failing to do the same. That so many people ignored his warnings drove him batty, and he eventually died in an asylum.

(It's easy to sympathize. In life, there is absolutely nothing more maddening than being the only person who understands what is really going on.)

So if sterilization wasn't the purpose, what was? Perhaps the goal was simply to have some warm water for cleaning the mother and child. A book called "A History of Childbirth" quotes a French obstetrician in the mid-1700s instructing doctors and midwives to use the household cauldron to "take the chill off" the water that will be used to wash the mother and child. So a full century, at least, before the advent of antiseptic techniques, water was heated when a woman went into labor.

And there's a good reason for using warm water to wash the baby: Newborns lack the ability to regulate their body heat. They have never had to worry about it, because they've been living in a consistently warm marine environment for nine months. If not kept warm immediately after the birth, they will turn blue. So the sheets are used to wrap the baby.

We still say, however: Don't try this at home.

Question: Why do countries still test nuclear weapons even though we already know that they work?

Answer: The problem with testing a weapon to see if it works is that if it does work, the weapon is vaporized.

Also, they seem to have so little suspense: We have never heard of a nuclear test that wound up a dud. They always blow up. You never see footage of anyone creeping up on a nuclear bomb that for some reason didn't go off. (The person who has this job steps very softly, on tippy-toes.)

Nuclear weapons haven't been used against an enemy since Nagasaki, but countries have continued to detonate them in "tests." The discovery of strontium 90 in cow's milk led to the ban on above-ground tests in the 1960s, but bomb-makers still blew up nukes underground, and only a couple of years ago did the United States and Russia agree to stop testing. France and China are still conducting tests.

The paramount reason countries test weapons is politics. You want your rivals to know that you can still achieve massive destructive power. The French, for example, constantly need to remind everyone that they are not just a bunch of effete snobs hanging out in cafes reading Camus.

There are a couple of practical reasons for tests. One is to develop a new weapon. The French this summer tested a new warhead that's slimmer and sleeker and thus, when it descends in the atmosphere, goes faster. The goal is to have a warhead that is harder to shoot down. The Russians maintain an anti-ballistic missile system around Moscow; the French think their faster missile can get through.

Another reason why tests are considered necessary is that the old parts on aging missiles wear out. Sometimes the companies that make those parts have gone out of business. Replacement parts from different manufacturers may not work quite right.

"It's much more complicated than an automobile," says Ernest Graves, former director of military application for the Atomic Energy Commission. "And if you put your automobile in a garage and left it there for 15 years up on blocks, I think you probably wouldn't be that certain that it would start if you came back."

The exotic materials in a bomb may also cause problems. A hydrogen bomb is filled with tritium, which is a form of hydrogen with two neutrons. Tritium can change with time: It can decay into helium. Helium is poisonous to a nuclear weapon because it soaks up the stray neutrons that need to be knocking around freely for a chain reaction to occur. So bombs have to be tested to make sure the tritium is sticking around and the helium isn't building up.

Naturally we know much more about constructing a nuclear weapon than we can reveal right here. National security, you understand.