A hollow discovery

Creeping forward from the exposed ledge, I noticed a deep, shadowy gap behind a stack of thick hardcovers. I slipped quietly inside, testing the narrow perimeter with the tips of my elongated fingers. The wood enclosed me on five sides, muffling the distant ambient hum of the house into a faint, rhythmic pulse against the floorboards. In the dimmest corner sat a forgotten glass marble. Curious, I extended a single claw and nudged it gently; it rolled an inch, striking the interior wall with a crisp, echoing click that resonated through my frame.