OK--so on a somewhat related note, I will now derail this thread entirely. ON a visit to Spain a few years ago, one of the people who was hosting me took me out into the field to show me some ancient ruins. While we were there, he showed me the local rock, and how easy it was to give it a couple of whacks and create a primitive knife. Very cool.

Before he threw the knife back on the ground, I asked if I could keep it, and tossed it into my shoulder bag. I also promptly forgot about it.

Four days later, I am checking through the security line in Frankfurt, and the alarms go off. I am pulled aside and they ask me what's in the bag. I have absolutely no idea what they are talking about. He grabs the bag from the outside and shows me there is something about five inches long there. I still have no idea. He asks me to slowly pull it out of the bag. I reach in....and realize that it's the damn stone knife!

With as much innocence as I can possibly muster on my face, I pull it out and hold it out flat on the palm of my hand. I look him straight in the eye and say: "It's a rock."

He looks at the knife. Then he looks at me. We lock eyes for a few seconds. He knows that I know that he knows its a stone knife. But it's a really rustic looking chunk of rock.

"OK," he says. "You can go."

I still have the rock!