I was thinking about this today.....

Let's say that I'm holding a rock in my hand and I drop it. When I drop the rock, not only will it fall to the ground, but the earth will, in fact, move up to meet it. Look at it this way: If I was holding a rock in my hand, and this rock had a mass that was equal to the earth's mass, then it would have gravity equal to that of the earth. So when I dropped it, because of gravity it would only fall halfway; the earth would move to meet it.

So when I drop this small rock in my hand, the earth is going to move (an unmeasurable amount) up to meet it. Interesting.