Chaos Theory (a.k.a. Unknown Origin) - S9-E1
Visible crew/equipment: While Gallant is running on the sixth floor the boom mic is visible in the window.
Tell Me Where It Hurts - S9-E7
Continuity mistake: In this episode Kovac has a patient who needs eye surgery. While at County General, Kovac says that the patient is 16 years old. Later, when Kovac goes to the golf course to get the doctor who does the surgery, he says the patient is 14.
No Good Deed Goes Unpunished - S9-E13
Character mistake: Dr. Corday finishes assessing a gun shot victim, then goes to the next trauma room to assess another. The steady cam follows her. She makes sure not to contaminate her gloves on the door, opening it with her elbows, but then goes straight to touching the next victim. Of course, in real life, she'd change gloves first. The shot never changes, so there's no chance of her changing gloves off camera. (00:12:30)
A Boy Falling Out of the Sky (a.k.a. Shifts Happen) - S9-E15
Plot hole: Dr. Lewis is talking to a patient about pets, and how she is "banned from a pet store" because she isn't good with pets. She explains that the only pet she ever had was sea monkeys as a child. But, in the earlier seasons, she had a cat. We actually saw the cat at one point when her sister was staying with her and let the cat out of the apartment by accident.
Answer: A man named Paul Sobriki comes into the ER in the season 6 episode 13 " All in the Family." He is complaining of headaches, Carter and Lucy decide to rule out meningitis and do a lumber puncture. Paul struggles during the procedure and believes that both doctors are stabbing him. Lucy, who is interested in Psych thinks something is wrong with their patient mentally, but Carter is dismissive of her. She gets cross with his attitude and she calls the psych department anyway to have a look at him. Later on and near the closing 20 minutes or so of the episode, all the staff start playing loud music and get a cake which appears to be blue lol, together to party as it's Valentines Day, Carter returns from somewhere and asks where Lucy is. He goes to check one of the rooms for her and Paul Sobriki comes up behind him in the dark and stabs him twice in the lower back, he collapses and as he falls unconscious he sees Lucy on the ground also. In the next episode, Be Still My Heart (ep 14), Dr Weaver discovers them and all of the staff work to try and save them, whilst Carter survives. Lucy's wounds are fatal and suffers a pulmonary embolism as Corday and Romano try to save her. Carter is grief stricken and feels guilty about the way he treated her, he becomes addicted to painkillers and Benton, Greene all help him and book him into rehab.