Continuity mistake: When Malik finds Carter's family noted amongst the richest in Chicago, he says that Carter's father is named 'Roland'. However, in later episodes, Carter's father's name is given as John Truman Carter, Jr.
Continuity mistake: Susan comes home carrying bags of groceries. When she first sees Chloe sitting at the door, a box of Kix cereal is on the side of the bag next to her body, but as she says "Chloe", the box is on the other side of the bag, away from her.
Continuity mistake: During the opening credits, when they are working on an unconscious patient, his belt is undone and his fly is down. A couple of shots later, the fly is up and the belt buckled, even no one touched them in between.
Doug Ross frequently hung his head low, appearing ashamed or thoughtful or privately amused, depending on the scene. This wasn't just an element of the character: George Clooney had taken to writing his lines on papers, sheets, and other props.