Spring Sesshin: Joshu's Mu

In this Teisho, given during the opening night of Spring Sesshin 2026, Rinzan Osho examines The Mumonkan: Joshu's Mu. Joshu answered the Monk's inquiry, "Does a dog have Buddha Nature or not?" by vocalizing the sound "Mu."  Mu translates as a negation: "No" or "Nothing." What is it that Joshu was pointing at? What is this Mu? How do we, as Zen practitioners use it to prod us toward greater intimacy with the ineffible.