Manda Bala, a penetrating new documentary by Jason Kohn about Brazil's recent slew of kidnappings and the intricate net of contradictions animating Brazilian society is a tortured study in tightrope walking. The story is similar everywhere in South and Central America: kids from rich families are plucked from standing traffic at gunpoint and soon a ransom is demanded. Sometimes, an earlobe will follow by mail, and other body parts, until the money is received.