Field guide No. 1459
Loose translation
The keys wore down into pebbles
An upright piano in a bare white room spills its keys across the concrete, and on the way they round off into black and white stones. The tune is still in there, now in river.
Field notePiano keys are wood and plastic; somewhere along the floor they wear down into beach stones.
Also possible, also breaking material
Ash flames bend without fireGrey ash holds the curl of flames above charred logs. All the fire, minus the heat.
Hedgehog with bubble tipped spinesSpines end in clear bubbles that ought to pop on the first step.
Hush moneyPurses hold coin; this one holds velvet. Odd currency, perfectly constructible.
Punching holes in steamPunch presses need something solid. This one stamps neat holes in a belt of steam that keeps them.