Final answer:
The story of "The Feather Pillow" involves a parasite as a creature, which typically feeds on the blood or bodily fluids of its host.
Step-by-step explanation:
The usual food source for the creature in "The Feather Pillow" is not specifically mentioned in the provided reference material. However, it is generally known that the creature referred to in the story is a parasite. Parasites like the one described feed on their hosts, which could be humans in the context of the story. Taking into account general knowledge, for the purposes of answering the question, the parasite's food source in "The Feather Pillow" would likely be the blood or bodily fluids of the story's characters. It's worth noting that the supplied references mentioning feathers, feeding tentacles, and various flora and fauna do not directly relate to the creature's food source in the literary context.