When Dr. Kovac, Abby, and others are wheeling a gurney into a trauma room, the patient sprays blood across Maggie Wyczenski's coat and the window of a nearby exam room. In the next shot, Maggie's coat is clean.
While talking to Maggie (Sally Field) just before the explosion, Noah Wyle visibly flinches, as if he knew the explosion was coming.
At around the 23:40 mark when Michael Michele and Eriq La Salle are talking and the camera is following them in a panning shot across the admit desk, when it passes Anthony Edwards, he looks up and directly at the camera.
When the bike trauma comes in and the lady who hit him came into the ER, she was holding her baby which was a brown skinned child with a lot of hair, especially in the back. They escort her back to the waiting area. After they finish the trauma and Luka goes to notify her what happened, her child is CLEARLY a different baby. The baby is lighter and the hair isn't as big. Guess they had to recast between shooting the scenes.