A beachcomber spots a blue stone among the pebbles, and a wave soaks their ankles just as they grab it. It turns out to be glass, a broken shard that the sea has tumbled until its sharp edges are gone. The poem pictures the bay as a gullet or gizzard grinding things down, and the speaker wonders what softer things the glass wore away as it spun. The stone dulls as it dries, so, wanting to show the children, the finder pops it in their mouth, where it shines like a gem again for a moment. Then it goes home in a pocket like a hard candy that never melts.
The mood is playful and quietly awed. The speaker seems delighted by small discoveries, and the poem treats something broken and discarded as a whole small world. Even the closing "taste of salted sun" suggests the beach lingers on well after the walk is over.