Continuity mistake: The HPD snipers watch McGarrett's office window, trying to get a clear shot at Collins. In camera views from inside the office, there's a coat rack with a hanger on it standing in front of the window. But in all the shots from the snipers' POV, the coat rack isn't there.
Continuity mistake: The bomber wants revenge on Danno for killing his brother, Joey Collins, whose death is recapped in flashbacks to a first season episode in which Danno first killed someone in the line of duty. But in that episode, Joey's name wasn't Joey or Collins - it was Thad Vaughn.