Continuity mistake: During the operation on the Asian girl from the market, a stitch breaks and Christina is covered with spurting blood, including all over her mask. When she turns to leave the OR, the all-over splatter on her mask has turned to dribble-like streaks instead.
Continuity mistake: When Addison first comes to Seattle, she mentions that she likes Derek's hair. She says it's longer than usual, looks like Russell Crowe. In the flashback of the night he left his hair long like it always is. Actually it seems a little longer in the past than current.
Revealing mistake: When Alex is talking to Rebecca Pope at the end of the episode, we hear Alex say "Now I know more about you than my friends." Watch Rebecca's left eye on the right if the screen when she says, "That's pathetic." Someone did a bad job of editing the CGI and we see a phantom eye over her left eyebrow.
Factual error: Derek performs CPR on Meredith in the back of the ambulance, but he does so incorrectly. He gives one breath and five compressions instead of two and thirty. Also, drowning victims need oxygen, and Derek should have used a BVM to ventilate Meredith, not mouth to mouth. Any doctor would have known how to provide proper treatment.