Rabelais's book opens with a cryptic allusion to a “sustantificque mouelle” hidden under the surface hilarity of his story and ends (if it was he who ended it) with an equally cryptic pronouncement by an oracular bottle. The penetration which is urged at the beginning—through fiber and bone to the marrow of truth which they protect—is evidently consummated at the end, the physiological turning into a geological image as Pantagruel and his friends penetrate the underground sanctuary where, in a flood of miraculous light, one may hear the word of truth, which is Trinch. The opinions of critics on this pronouncement range from considering it an absurd joke to a grave and specific allegory of one thing or another. Similarly, the substantific marrow which Rabelais promises us at the beginning is taken by some as a joke which hides a truth and by others as a joke that hides nothing but another joke. Most agree that there is a mixture of joke and seriousness in Rabelais's book, but some insist on a complete disjunction between the comic and the serious, while others argue for a close interpenetration.