how is Renfields bizarre behavior significant to the story?

Dr. Seward reports on the strange behavior of Renfield. Renfield is fascinated by animals that devour each other. He catches flies and feeds them to spiders, and he also eats the insects himself. He catches some sparrows and begins feeding the spiders to them, and he eventually asks Dr. Seward if he can have a kitten. Dr. Seward refuses. The next day, the sparrows are gone. Dr. Seward asks where they went, and Renfield responds cryptically that they all "flew away," but there are feathers around the room and blood on Renfield's pillow. Later, he vomits up feathers.

Renfield's behavior parallels Dracula's need to absorb life. Renfield longs to be a being like Dracula, and later the madman will become Dracula's henchman. Dr. Seward's journal entry touches on the important theme of madness. Madness is a kind of creeping threat throughout the novel‹the heroes will plan their counterattack against Dracula within the walls of Dr. Seward's asylum, a place where madness, though contained, surrounds them (Hindle xxv-xxvii). Throughout the book, madness and the supernatural are always threatening to invade the order of sane, "natural" lives. Both forces threaten the stability of the characters' normal English lives, and Seward's strange envious comment about Renfield hints at the slippery nature of the divide between madness and sanity.