In saltwater aquariums.why do feather dusters "smoke"?

what do you mean by "smoke" the only thing i could think of is when you feed the feather duster or corals, they release a mucus/slime to remove any access organic/food materials left. it usually looks clear and floats above the coral or feather duster making the illusion of smoke. i see my corals and feather dusters do this when i feed.