Instead of the usual pale, dramatic spirits, the speaker imagines ghosts as oddly humble things: white and watery like boiled potatoes, shimmering like the moon in a ditch, missing their eyebrows. The comparisons are funny, but they also make the ghosts feel a little pitiful. Nothing about them is grand or frightening.
The poem gets more interesting when the ghosts leave the graveyard for banks and stock exchanges. The poem suggests these are places where people feel hollow or drained, so the ghosts seem to belong there more than among the tombstones. Then the tone shifts. They step into traffic "like swimmers into a cold mountain lake," as if they don't quite grasp danger, or simply don't mind it. They can only murmur "Ah," a sigh that could mean wonder or weariness.
The final line is the sweetest and saddest: they would be afraid of the dark. The mood is playful and tender, with a quiet ache underneath. The ghosts end up feeling less like monsters than like lost, frightened people.