Some questions have no answers. We will never know, for example, who--besides calves--came up with the bright idea of drinking cow's milk. Tell the truth: Do those udders look appetizing to you?

And while we're asking, who first thought to make bread with yeast?

If you've ever seen yeast, you know it's a sand-colored, lightweight, powdery substance. It looks a lot like beige dust.

It's remarkable to think that about 4,000 years ago, someone discovered that if you put this weird substance in water and added a little sugar, it would get foamy. It's even more remarkable that they then took the next step and kneaded this mixture with pulverized grain. And it's simply astounding that they figured out that if you let this stuff rise not once, but twice (or even more times) and cook it in a hot oven, you can make bread.

We take things like bread and milk for granted today. But without vision and courage on some anonymous ancestor's part, lunch would be a lot less interesting. We owe a debt of gratitude to these food soldiers of the past, who bravely figured out what was safe to eat and what wasn't.

If you're feeling at all wistful for a time when you could be a hero just by eating, here's something that might make you feel better: Food still has the power to kill you.

The murderous agent might not have fangs and claws. It might not even be visible to the naked eye. And, most exciting of all to the adventurer inside you, it might be lurking in your kitchen.

That's right. Your very own refrigerator might be harboring evil in the form of molds and bacteria. How can that be, you wonder? You're a clean person and an excellent cook--what would make your good food go bad?

As it turns out, microscopic evil lurks everywhere. And it's just waiting for a chance to turn your food stinky and blue.

Here's how the horror happens.