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The coffee shop scene where Brad Pitt and Angelina Jolie confront Vince Vaughn was filmed in the same coffee shop as a scene in Old School (2003), also starring Vaughn and Perrey Reeves. A coffee shop scene in Gone in 60 Seconds (2000), where Nicolas Cage talks with his mother, Grace Zabriskie, also used the same location, and also starred Jolie.
Brad Pitt reportedly left the project after Nicole Kidman dropped out and her replacement had not yet been found. Once Angelina Jolie signed on, he returned to the project.
When Jane is going to her first shown kill, she correctly answers a question from the quiz show Jeopardy! (1984). This was unscripted and spur of the moment on the part of Angelina Jolie.
In one scene, Benjamin Danz (Adam Brody) is wearing a Fight Club t-shirt while being interrogated by John Smith (Brad Pitt). Pitt starred in Fight Club (1999).