Faces don’t get much more expressive than Bernard-Henri Lévy’s. The thick eyebrows go up and down, powered variously by rage, incredulity and sadness; the lips purse, pout and curl with derision. But when the 75-year-old French philosopher describes the scene at what was left of the Kfar Aza kibbutz in southern Israel on October 10 last year, his face empties of all expression.