Revealing mistake: Near the beginning of the show, Mark's father puts a bulb into an old slide projector. Then there is a small explosion with smoke and flames - watched carefully, we can see are actually coming from the other side of the projector - the flames can be seen shooting parallel and close to the floor, which wouldn't have happened if the explosion actually came from the projector.
Revealing mistake: After Mark gives his father the keys and tells him to park the van, in a following shot when Elizabeth joins the gurney rush with Carter, as she's walking backwards there's a distinctive large bulge at the back of her waist from the mic transmitter. (00:10:55)
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.