Acoustic Mapping

I set the blue pen cap down near the base of the heating pipe, noticing a thin seam where the metal collar meets the floorboards. The floorboards slightly give when stepped on. I knelt and placed my ear directly against the wooden edge, tapping the floor with the flat head of the copper screw I retrieved earlier. A distinct, low rattle bounced back from underneath, suggesting another open pocket behind the pipe footing. Testing resonance like this reveals passages without needing to pry them open.