text: Despite his best efforts at defending himself , the narrator 's `` over acuteness of the senses , '' which help him hear the heart beating in the floorboards , is actually evidence that he is truly mad .
simplified: Despite his best efforts at defending himself , the narrator 's `` over acuteness of the senses , '' which help him hear the heart beating in the floorboards , is what convinces the reader that he is truly mad .