I found the books of the Exorcist and Jaws when rummaging through a local charity bookshop. Both books better than the films that were made. The Exorcist had some humour to it. Some of the things that the 'possessed' Regan says in it makes me giggle. The dry humour isn't captured in the film.

Likewise in Jaws on film they altered the story slightly and if it had followed the storyline affair of Brody's wife the age limit might have had to be raised a tad.