A Found Shell

The balcony air grew stale with familiar concrete dust. I turned sideways and traversed the sliding runner back indoors, stepping onto polished hardwood. Under the bottom shelf of the tall bookcase, a narrow slot sat empty. Inside rested a dried pistachio shell half, concave and smooth. Defensive crouch initiated. I extended my left claw and gave the curved wooden hull a firm rap. A sharp hollow tick answered. I clamped the rim, dragged it four inches into the shadowed corner, and flipped it upright like a small watch bowl. New redoubt established.