A scene was shot in which Illeana drives back to her house with the old pick-up and a branch from a tree falls and breaks the windshield. It took several takes to get the shot, and apparently destroyed the last remaining windshields for the pick-up available anywhere in North America at the time. The scene was not used.
The source novel's character equivalent to Illeana is James Costa, a British museum curator. Martin Asher's analog is Martin Arkenhout, a native of Holland. The prime settings of the novel are England and Portugal.
There is a part, when the mother of the murder is being interviewed, where she states she saw pulling on his ear. She states, "And he was pulling on his ear. It's an old nervous tic from childhood." I went back and watched the movie and found that there is a scene at the bus stop, right as Young Asher (Paul Dano) is buying a bus ticket, you see him pull his ear, he again pulls his ear right before he kicks his travel companion into the passing truck during the tire change. Additionally, Costa (Ethan Hawke) holds it together during the interrogation scene (because he is not nervous) but as he begins to flirt with Illeana (Angelina Jolie), during the story of the man who painted on a door, Costa pulls on his ear. When interviewing the man on the train he is about to kill, Costa pulls on his earlobe once again. I Googled this little Easter Egg, and found nothing. I think I am the first one who noticed this treasure the director must have intentionally directed the actors to do. It only happens 3 times that I noticed, which is enough to catch it, but not enough to give it away or make it obvious, brilliantly done.