That, and its bare teeth reminded me a bit of the Mouth of Sauron, from the scenes that were cut from the Lord of the Rings film trilogy by Peter Jackson.

Similarly in how the Gravemind is but the brain and mouth of the Flood, I got similar vibes about him being just one being out of the billions that it had consumed a hundred thousand years ago, and of the Precursors that made and chose to end sentient life.