RALPH: A harrow was a farm instrument consisting of a wooden beam with iron teeth sticking down that would be dragged over a field to break up clods of dirt, turn over the soil, and cover the seed. You might imagine here a very wide rake. So to harrow meant to drag this tool across a field.

SARAH: Shakespeare uses it in Hamlet in a new, metaphorical sense, meaning to break up and turn over the soil of the mind, to tear someone up psychologically, to cause them pain or distress. The ghost uses it here, but the word has already popped up in the very first scene of the play, where Horatio says, referring to the earlier apparition of the ghost, "It harrows me with fear and wonder."