Continuity mistake: As Cameron is questioned about the girl that commited suicide, the interviewer holds a photo of one of the mostly-black posters. When we see his view of the photo, the white letters spell 'DAN', but before and after that shot, when we see his face, we can see through the photo, and it only reads 'A', which is a different poster seen earlier in the same episode.
Revealing mistake: Look at Summer Glau's face when she jumps off the Jeep onto the black van and punches the windshield to throw the driver out - it isn't Summer Glau. It's her stunt double, Sonja Munsterman. It isn't even Lena Headey driving the Jeep or Thomas Dekker sitting in the back.
Character mistake: When Dixon arrives to find Derek lying on the table with a serious gunshot wound to the chest, he immediately begins giving Derek chest compressions - without doing even the most basic assessment of Deker's condition, verifying whether he is breathing or even has a pulse. Dixon is a trained Emergency Medical Technician, not a passing samaritan. His error is against the most basic rules of his profession.