A railroad is hauling dynamite. A strike against the railroad leads to violence. In a confrontation, someone fires a rifle at one of the cars carrying the dynamite. A massive explosion ensues. A bystander is injured by the blast.  Absolute liability? Assume that the railroad did nothing unreasonable in the  way it stored and hauled the dynamite. Is this "the kind of risk which makes the activity of blasting ultra-hazardous"? What about the rifle shot into the dynamite?