Continuity mistake: In the teachers' lounge Jack tells Chase that the second floor is cleared. When he doesn't get an answer he realises something is wrong and runs down to the floor Chase is searching. After he's cut Chase's hand off he runs out into the hallway and into the lounge which is suddenly on the same floor Chase was on.
Factual error: Chase gets into surgery way too quickly. Considering the time it would take for the paramedics to reach him, stabilise him, pack his hand in ice and bring him to the ER, and then for the doctors to get him ready for surgery, sedate him and actually start operating. There is no way they would have been able to do that in the amount of time they did.