Owner of a Lonely Heart - S2-E11
Continuity mistake: When Christina is in the locker room eating a packet of crisps, everyone comes in and she asks them if they have any decent food. In the next shot you can see she is now holding an opened bar of chocolate. Then in the following shot we actually see Meredith hand her a wrapped bar, which Christina then opens (and the previously opened bar is gone, of course.) (00:03:40)
Owner of a Lonely Heart - S2-E11
Continuity mistake: Olivia walks into an elevator with Izzy already inside and they go up 3 floors. When Izzy leaves the elevator, it's the same floor from which Olivia came (same equipment and decor).
Owner of a Lonely Heart - S2-E11
Continuity mistake: When Dr. O'Malley is talking with Carl Murphy in his room, the position of the circle of containers (with the leeches inside them) changes between the shots during the scene. (00:32:10)