A gray flint pebble holed clean through by the sea alone, strung on waxed leather: the hag stone, an old British threshold charm for doors, windows and dusk.
At a glance
Hold it to one eye at dusk and look through. That is the old custom with a hag stone: a gray flint pebble bored clean through by nothing but the patient work of water and time, strung on a length of waxed leather cord.