“MUCH HAS BEEN WRITTEN ABOUT the quaint and lumbering buopoths native to the Exilic Lands and other curious places – but to this day, little remains understood about the shy beasts beyond the proverb that ‘they will haul all day on a fatberry-cake and a kind word.'” — from Road Bound
That’s the in-universe explanation from one of my Prosatio Silban stories. Outside the stories, it’s a different matter entirely…
In former dreams he had seen quaint lumbering buopoths come shyly out of that wood to drink, but now he could not glimpse any.
And that’s it. That’s the only description we have, from the man who invented the beasts: they are shy, quaint and they lumber. Although the latter suggests a possessor of sizable proportions, we have no real idea of what they look like nor what are their other habits / qualities. (We don’t even know how to pronounce their name — BOO-owe-pawth? BWO-poath? BWA-pawth? It’s a mystery.)
Now, fen (fanspeak for “fans”) being fen, there is always a tendency to embroider a beloved Thing and, in so doing, make it a bit more real. (To other fans, anyway.) HPL fen are no exception. The “Old Gentleman from Providence,” obscure in his own day, is at least secretly famous in ours; his tales and the critters therein have sparked a modern industry of role-playing games, in-depth critiques, plushies, fan- and pro-fiction, and other such stuff as befits a much-admired literary locus. (Including, in my case, loving homage.) Buopoths are part of that mix: a simple Google image search will disclose hypothetical animals of all sizes and shapes, colors and pelts. But as I said, nobody can agree on what they “actually” look like.
Because of this imaginary consensuslessness, “my” buopoths — the Exilic Lands’ buopoths — are thus polymorphs, shapeshifters, things-of-no-determined-form. And the buopoth who draws the Cook For Any Price’s galleywagon is named Onward, because … well, that is its name.