During “The Artist Is Present,” Marina Abramovic is chairbound for as long as nine and a half hours. A furious debate has ensued: How does she pee? The art writer Mira Schor has offered a fellow artist’s theory that Abramovic’s dress is outfitted with a catheter that feeds urine into sewn-in receptacles. Others suggested an adult diaper. In a preshow interview, Abramovic said that a bedpan had been built into her chair; it was ditched early, though, after the vent tailored into her dress irritated her skin. So what’s the answer? Her assistant Danica Newell insists that she just holds it in. Note to aspiring artists: Dehydration and muscle control are a must.