Further speculations on this: I think the "you are what you eat"/chameleon theory must be a part of the Rajan's threat to the inhumu and therefore their secret---this seems to be a part of what Krait must have told him as he was dying. When he reasons that they hibernate and are very weak when unearthed, and captures Jahlee, he offers her a cow to break her fast. Could it be he has figured out that, after hibernation, they have begun to lose their intelligence and human shape as their bodies use up all the human blood/DNA they've ingested, and that if captured in their famished state and offered a cow, that they'll feed ravenously and perhaps adopt a cow's low level of intelligence and docile nature? I admit I don't have a lot of textual basis for this---does Jahlee seem "dumber" after she drinks cow's blood? (But the Rajan doesn't let her drink her ravenous fill---perhaps because he wants her intelligent enough to parley with and do her dirty work against the Hannese?) She does seem to assume a human shape pretty quickly, however, so that ability yet remains. I dunno....idle speculation, perhaps. I think Gene has simply withheld (or just not emphasized enough) a few vital clues that would help us all peg the Secret exactly, so: sweet misery until the next book....
What do you think of this angle?
-Ram
*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun.