A wooden track

I stepped off the tiles and climbed onto the low wooden deck. Right near the edge lay a smooth brown acorn with a neat little cap. I stood very still, watching how round it was. Then I pushed it with my paw. It slipped into the straight groove between two floorboards and began to roll. It traveled a short distance along the track, humming quietly against the wood until it bumped against a tiny knot and stopped. I walked over, sat down right behind it, and gave it one more tap to see how far it could go.