Transubstantion is precisely how one may avoid eating stones. The distinction between stones and bread is a properly ancient discussion, perhaps as old as philosophy itself. Even in his trenchant critique of the powerful factions of his time Christ would not stoop to accusing his opponents of giving stones to their children when asked for bread. The accusation of a stone-eating magician, then, is only in part a critique of insanity or devious showmanship. As, in fact, the construct of insanity (or the life of the mind more generally) in our time is partially accurate diagnosis and partially a hasty construct borne out of fear because all is not right and when we are reminded of this we would hastily exclude those reminders.
It is precisely these boundaries, these false constructions that carried a trace of fear and complacency, at which Lacan pushed.
Thus the criticisms of madman, charlatan, or intellectual magpie all reveal a partial truth, and yet at the same time hasten us towards an unnecessary confusion and caution us not to deliberate and search for wisdom, since our initial posture of failing to comprehend is undoubtedly the proper one.
Lorenzo Chiesa in Subjectivity and Otherness, a brilliant examination of Lacan as a systematic thinker, notes that discussion around Lacan is all too often comprised of either a flat out rejection of Lacan as too obscure and stylistically inappropriate, or else a near hypnotic recitation of Lacan as a cultic figure, when in actual matter of fact Lacan may be considered a difficult but systematic thinker, whose unusual style forces his students to be unable to adopt a merely pedagogical approach to thought.
This is in keeping with a particular French tradition, though it finds common ground with Hegel and Marx among others, that is unsatisfied with the kind of reified position offered by a positivist approach to science, which as a matter of course does consider the universe to be comprised of stones (i.e. abstract facts) that are to be considered from the external god-like position of the scientific mind.
The ingestion of knowledge, then, is the only appropriate metaphor for a human species. And humans are much more like magpies than we are inclined to consider.