Continuity mistake: Romano is standing outside an ER room watching through the glass. To his left, down the hall, we can see a woman pushing someone in a wheelchair. But when the shot goes to him entering the room, there's an extra behind him on the left pushing a large cart of supplies - there was nowhere for him to come from.
Continuity mistake: Mark comes into the cafeteria with a sytrofoam bowl of something, and when he sits down he starts to take the lid off. The next shot shows him already eating it with a spoon - there was no time to accomplish this so quickly.
Continuity mistake: When the "accident" victims are brought in near near the start of the show, a woman wearing overalls is covered in masses of glistening blood in the closeup - but the wider shot shows less blood and it is much more dried on her clothing.
Continuity mistake: Lizzie sees Dr. Morgenstern for the first time in the ER and she asks Kerry, "Who the hell was that?", and Kerry answers, "Our Chief of Emergency Medicine." Yet when he resigns in Episode 19, he tells Peter he's resigning as Chief of Surgery. Unless he held both positions, Kerry's answer could not be considered a character mistake, as she would have known what his position was.
Continuity mistake: Near the beginning of the show, Peter is feeding Reese in the hospital cafeteria. Reese has a bowl of pablum that is in the middle of his high chair tray. The next shot shows the bowl way over to the left, even though there was no time for the change in position.
Continuity mistake: When Doug is sitting at the cafeteria with Mark, Peter and baby Reese, his arm is stretched out on the table as Peter says, "fifteen minutes of quality time". The shot changes and suddenly there is no sign of his arm.
Continuity mistake: Just before Peter bends over beside Reese, an extra is starting to walk behind them. The next shot shows the cereal on Peter's head and we should be able to still see the extra, but there's no sign of him.
Answer: Take care of your dad.