This has absolutely nothing to do with this scene but is at least tangentially related to the Thriller Bark arc so I'm gonna share it anyway. The word galvanize is an eponym derived from Luigi Galvani, who was a scientist and physician in the 18th century who helped pioneer the field of bioelectricity when he discovered that he could make dead frog legs move when ran through with an electric current, with later proponents of his work going so far as to shock human corpses attempting to bring them to life. This breakthrough would in part inspire the creation of Mary Shelly's Frankenstein, which, some two hundred or so years later would in part inspire Thriller Bark.
So in a way I guess you could say Hogback has galvanized these corpses, albeit with shadows instead of electricity, forcing them to move without recreating true life.
