Doctor Who: 14 Cool Details In Steven Moffat & David Tennant's Silence In The Library Commentary

Once one of those "secret buttons" has been pushed, a load of books come flying off the shelves in the main library room, narrowly missing most of the characters in the scene.

However, these books do not miss the Doctor, who, at one point, has one launched directly at his right shoulder (you can just see the book in the above image).

So was this an accident? Nope. Tennant actually asked one of the prop guys to throw a book at him, simply because he thought it would be "good" for the scene.

As for the rest of the books, some of them were fired from the shelves with air propulsion, while others were simply thrown by the crew.