The speaker is lying next to someone, talking softly about "sometimes-things": objects that blur into the background, barely drawn, not meant to stand out. Most of the time they're just things. But now and then they seem almost alive, not because they move or speak, but because they lie so still while seeming to hum or tremble inside, like a string still sounding after everyone has stopped listening.
What the speaker feels is a mix of longing and self-doubt. They suspect they're foolish for imagining life in objects, and they sense these things hold more meaning than they can reach. They want to catch up with them. The poem ends with a wish: to live a little like these things, at ease with stillness, and not to be afraid of eventually lying down beside them.
The mood is hushed and intimate. The interruptions to the listener ("are you still listening," "no don't get up") make it feel like a whispered confession in the dark, tender and a little uncertain.