A Gentle Teeter

I shuffled back inside to the coffee table... was that long wooden ruler waiting for someone? A fat, round cork was resting right near the center of the wood. Very carefully, I pushed the ruler with both paws until it lay straight across the curve of the cork. It tilted immediately with a muted wooden clack... tap. I held my breath, then pressed one cautious paw onto the raised end. It dipped down so smoothly, sending the opposite side floating into the air! I nudged it back and forth, listening to the steady, hollow rhythm against the table. Did I just build my own little seesaw?