“It was not unless one lifted one's gaze from all the allegedly normal events occurring before one's eyes and looked at the executioner's sword hanging over everyone's head that the normality was revealed as a sort of mass insanity. . . Passengers on a ship who are . . . engaging in all the usual shipboard activities appear perfectly normal as long as their ship is sailing safely in quiet seas, but . . . deranged if in full view of them all their ship is caught in a vortex that may shortly drag it and them to destruction.”