To my ears, a lot of detail is hidden in "knowing what makes itself tick". The limit of human Umwelt, cognitive closure, is an arena I find fascinating.

Modern people tend to identify understanding with mechanistic explanations. Veins, glycogen, immune states, hoof pumps. These are interesting and satisfying to us. But does that kind of explanation satisfy only because we are apes with ape language and interests, leaving aside even that we live in a society that values those explanations?

If a horse-level intelligence existed, perhaps its most satisfying explanations would not be "I can inspect the venous plexus in my hoof," but something else. Maybe more proprioceptive: pressure, load, gait. Or maybe that's just still my primate prejudice poking through.

What would satisfy a horse scientists might seem opaque or insufficient to us, but maybe our biochemical account would seem equally beside the point to it?

Maybe there is no species-neutral answer to what counts as understanding what one is.

On a deeper level, I suspect that a "complete understanding" in an absolute or divine sense is infinite. Our perceptions are necessarily limited, only a model of reality. In order to understand in a way that helps us survive, we must filter out a lot of information that is not absolutely irrelevant, but is irrelevant to us. Even Funes remembered only that which is relevant to a human, that which he could perceive in the first place. He could not remember changes in magnetic fields, background radiation, subtle shifts in gravity.