If Silas is neither dead or alive how can he feed Bod? And is there no in-between with dead and alive?
In this most unconventional tale, Silas is the favorite of Bod's tutors; however, as a being who is neither alive nor dead, Silas has responsibilities in the other world that he often must attend to, so he passes between both worlds, the natural and the preternatural. When Bod talks with Silas he asks,
"How could you do that?"
"Some skills can be attained by education, and some by practice, and some by time. Those skills will come if you study. Soon enough you will master Fading and Sliding and Dreamwalking."
Neil Gaiman, the author, writes of Silas, "He would be there waiting at sunset, just before Silas awakened."
Then, in Chapter Seven, Silas talks with Bod, telling him he is to stay in the graveyard where he is save because the murderer of Bod's family is still looking for him. Impatiently, Bod replies,
"Well, you aren’t alive. And you go around and do things.”
“I,” said Silas, “am precisely what I am, and nothing more. I am, as you say, not alive. But if I am ended, I shall simply cease to be. My kind are, or we are not. If you see what I mean.”
Bod answers that he does not understand. Since Silas never "gets into trouble," the reader may assume that he is a vampire; but he is a member of the Honor Guard. He has spiritual capabilities such as the power to erase memories, Yet, he arises at night; he has "a fingernail as sharp as a blade" and he only consumes one food, "and it was not bananas." Then, in Chapter Four, there is the sound in the belfry of velvety wings and "Silas left his resting place and clambered head flits down the spire."
While Silas is out in the natural world, he probably gleans food for Bod from the homes of his victims.