Patrick Bateman: I think, um, Evelyn that, uh, we've lost touch.
Evelyn Williams: Why? What's wrong?
Patrick Bateman: I need to engage in homicidal behaviour on a massive scale can not be corrected but, uh, I have no other way to fulfill my needs.
In the scene after Patrick Bateman's second encounter with the detective in his office, we see Bateman having sex at Courtney's apartment. After he rolls off her, Bateman approaches the large, stand-up mirror in the bedroom. In the upper right hand corner of the mirror, a boom microphone can clearly be seen moving around to pick up Christian Bale's lines. The next time we get the same long shot, the microphone is gone.
Willem Dafoe was asked to play Donald Kimball in 3 different ways: he thought Bateman was guilty, he didn't think Bateman was guilty, and he wasn't sure if Bateman was guilty. They were all blended together to make the audience not know what Kimball thought of Patrick Bateman.