Continuity mistake: Just as the episode starts, Dr. Troy is reattaching a thumb and some fingers to a patient. Liz then tells Dr. Troy that he incorrectly placed the middle (longer) finger where the index finger should be. As she says this, the camera shot of the hand from a few feet away shows that the fingers ARE correct, then the following close-up show shows the fingers attached wrong, not to mention if you look real close during this shot, the fingers flinch a little.
Continuity mistake: During the scene where Sean and Megan are talking on the bench after abruptly leaving the restaurant, pay attention to Sean's arm as it is around Megan. It changes positions several times around Megan's back and shoulders during different camera angles, and he never noticebly moved it.
Answer: It's a computer graphic.