Continuity mistake: When the family goes to throw Carla through the window, watch the window they throw her towards. The window is made up of at least three sections of glass, each no more than 2-3 feet wide with metal posts between sections. When the shot changes and Carla (well, the dummy of Carla) hits, the window is now only two sections, each about 5 feet wide. The easiest way to tell is watch the metal post farthest to the right. When the shot changes to outside, that post, which should now be farthest to the left, has vanished.
Continuity mistake: During the scene where the class is being warned about the dangers of being a "wait and see" type of doctor, JD imagines himself as being the only person in the auditorium. In the first shot of him alone, there is a bookbag (or something similar) sitting on a seat about three seats to JD's left. In the next shot of him, it is gone, and in the third and final shot of him alone, it is back again.
Continuity mistake: When J.D lends his nasal spray to Doug in the final scene Doug returns the spray to J.D after putting the cap back on. In the very next shot as J.D says "Don't bogart my nasal spray", J.D uses the spray without putting on the cap, and you can see the cap placed on Doug's tray.
Continuity mistake: When Laverne does a slam dunk, you can see that the ramp leading to the hospital main entrance has no-one standing on it or in front of it. But before and after the slam dunk you see see two doctors with a basketball on the ramp, and Franklin standing remarkably still, with a camera, in front of it.
Continuity mistake: In the scene where Turk, JD and Dr Cox are talking about women, and how many they've slept with, take a look at the items on the table in the background that Dr Cox was previously sitting on, they appear and vanish. Mainly the cup and napkin dispenser appears and disappears in between shots.