Continuity mistake: We see a nurse writing down "Yang, C" on the assignments board; note the handwriting. Later, when Burke notices that Christina's name is on the board, the handwriting of "Yang, C" is completely different and other minor writing differences are noticeable too.
Factual error: Derek tells Meredith to do an MRI on the lady that has a fork stuck in her neck. But an MRI-machine is actually a huge magnet; that's why there's absolutely no metal allowed inside of it. Doing an MRI on someone with a fork stuck in her neck is extremely dangerous.
Continuity mistake: The scene where the bomb explodes shows the bomb squad captain walking toward the end of a hallway. Just as the bomb explodes you can see he is about 5-6 feet away from the end of the hallway where another bomb squad tech is waiting. After the explosion the scene cuts to Meredith flying backwards then to a shot of windows being blown out then back to a rear shot of Meredith hitting the floor. Notice here that a second floor is not visible at the end of the hallway. The scene finishes with a final aftermath shot of the hallway as the debris settles. Here we see an entirely different hallway with a visible second floor and the end of the hallway extended by about 10 feet.
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.)
Continuity mistake: When Derek sits in the rocking chair in the room with the premature baby and then Addison starts listing their relationship options, the blanket hanging over the back of the rocking chair constantly changes position, evident by the green stripes on it.
Continuity mistake: Cristina walks in during the party with two containers of cupcakes, places them on the side table and walks out. When Alex opens the lid and starts picking at the cupcake toppings, in the shots facing him the top container lid is wide open, but in shots facing Meredith the lid is closed and the cupcakes are untouched.
Continuity mistake: At the very start of the episode when it shows Burke laying on the floor after being shot, there is a very large pool of blood with his glasses right next to the blood. But in the next shot there is no pool of blood anymore but it returns in the next. Additionally, the pair of glasses change position.
Continuity mistake: When Christina notices the bomb squad moving Meredith down the hallway with the gurney, she leaves the room and removes her scrub jacket and hands it to a nurse. When she is out in the hall and reaches them, she suddenly has the scrub jacket back on again.
Continuity mistake: When Meredith puts the Hello Kitty plaster on her forehead in her car, she puts it on upside-down. When she reaches the elevator it is now on the right way up (it is unlikely she would have removed it just to place it back on the right way up.) In addition when she is in the elevator, from shot to shot the position of her fringe (and how much of it covers the plaster) keeps changing.