A distant ship

 You ever hear a lyric that sounds like a whole world?

"A distant ship smoke on the horizon".

It sort of comes out of nowhere in Comfortably Numb. There's no other mention of ships, horizons, seafaring. Maybe it links to the "waves" in the next line -- It's purely a metaphor for some trouble or pain now being distant and no longer relevant except for it very slowly washing up on your shores -- but I also love the way it causes a mental image to flash in front of your eyes.

There is no pain, you are receding. Ok. More medical stuff. And then -- a distant ship smoke on the horizon. Look. You can see it, right now, a little ship, way off, barely perceptible, with a small plume of black smoke drifting away from it into the darkening blue skies above an impossibly huge, a comfortingly huge, ocean. It bobs around on the currents, detached from whatever turmoil is going on back on land. 

I sometimes wonder if it's referring to a painting the protagonist saw in a doctors office as a child. After the waves line he leads into a half-remembered memory of an illness as a child. A fever. A fleeting glimpse. The painting burning into his memory forever through the formative and traumatic trip to the emergency room. 

You can imagine that image, the painting, the ship, returning to his fevered mind as an adult. He lies back and goes into a Proustian stupor, instead of a biscuit (was there more to Proust than the biscuit?) it's the numbness of narcotics. They, obviously remind him of being an ill child (or just a child, The Wall seems to be entirely about adults dealing with childhood trauma), and that's where the painting of the calm, soothing ship appears in his mind and he slips back into the haze.