...having a quick beer-thirty IPA at the bar next to my office, and jotting ideas in my notebook, trying to come up with a few more items/ideas to populate my shared hex for its next draft...
The guy next to me (whose beer-thirty arrived had a substantial head-start on mine) looks over and says, "Hey look, we're both doodling!" (he is sketching on a notecard while half-listening to his lady-friend). "Whatcha drawing?"
I tell him I'm making notes for a wilderness adventure story, but that my forest is boring.
"Oh, you need to make it underwater."
"I have a lake with some interesting stuff already."
"No, dude, like filter feeders. Saw them on TV. Put 'em in trees. Guy's in the forest, it's all dark and creepy. 'Hey, what's that?' Sees something floating in the air. 'Rawr!' "
And that is how I came to contemplate arboreal filter-feeders....
... another thing perfect for eating halflings.