We've all had that moment. The moment where you might see or hear something and you wonder: Am I going crazy? In this hour, TED speakers share their experiences straddling that line between madness and sanity — and question if we're all in the gray area between the two. Neurologist and author Oliver Sacks considers what hallucination reveals about our minds. Legal scholar and author Elyn Saks (The Center Cannot Hold) presents a tale of mental illness -- from the inside. Comedian Joshua Walters muses on mental illness and mental "skillness" -- being just crazy enough. And writer and documentary filmmaker Jon Ronson explores the strange world of psychopaths.