Pressing a shell to his ear, the speaker hears not just the sea but a whole desolate world: a sunless, wind-swept shore that has never known human presence. The sound becomes a low, sad murmur of pebbles endlessly rolling, slimy seaweed swaying, and blind waves moving through endless twilight. There is no day or night, only a cold, eerie half-light and a wind that seems almost afraid. The mood is bleak, lonely, and unsettling, as if the shell opens onto a place outside time.
Then the speaker lowers the shell, and the ordinary clatter of a cart in the street feels suddenly sweet. That final contrast brings relief: the real, imperfect human world is far more welcome than the cold, timeless emptiness inside the shell.