There is not much difference between the two. I would say that one of the major differences between the two is that the book is devoted to the idea of exploring Starling's apprehension of Buffalo Bill. The film does the same, but I think that there is a greater aspect of social concern in the film regarding Starling's role as a strong female. The film does a very good job of exploring the barriers that she, as a woman, must face in apprehending Buffalo Bill. It doesn't belabor the point being made, but shows it subtly, to a point that the book does not. Even in the opening titles sequence in showing Clarice boarding an elevator with all men and receiving slight glares, or when briefing the West Virginia police, as well as other moments where Clarice the special agent has to battle against being seen as Clarice the woman. This is really expanded when it seems as if the only person of mention to treat her as an equal would be Dr. Lecter, who exposes her psychological terror. I thought that this was brought out nicely in the film and not something that occupied the thoughts of the book.