In 1987, the Israeli human rights attorney Felicia Langer was paying a visit to the Neve Tirza women’s prison when a client named Siham shared some disturbing news: the prisoners held there had recently been sprayed with a chemical agent that left them writhing on the floor. Langer grabbed a tissue that had been exposed to the substance – a piece of evidence, perhaps, in a future legal case. Then, on impulse, she lifted it to her face and inhaled deeply. Her hope, she wrote later, was that doing so might enable a doctor to identify the toxin.This anecdote appears...