The Magnetic Riddle

A flat bar magnet was resting beside an open wooden toolbox on the bench. Right next to it lay a shiny steel washer and a smooth grey pebble from the garden path. Could the heavy black bar pick up both? I paused, holding my chin to ponder the riddle. I nudged the smooth pebble against the dark metal first—clack, nothing, it just rolled away! But when I slid the washer close, snap! The magnet snatched it right out of my fingers with a sharp click. I tried balancing the pebble on top of the sticking washer, and to my surprise, the little metal rim cradled the stone like an eagle's nest.