According to Osho, Buddha conveyed to Mahakashyap not a verbal message but the ineffable truth—silence itself—transmitted beyond words through presence and a flower as symbol. Everything sayable went to others; the unsayable was given to Mahakashyap, who could understand silence. This is the 'secret of the secret': direct, wordless realization rather than conceptual knowledge.
Buddha gave Mahakashyap a silent knowing you feel inside, not something you can say.