Visible crew/equipment: When Jack, Kim and Teri are at the compound, Kim stands up shortly before Gaines' first shot. On the left you see a crew member kneeling. (00:26:20)
Continuity mistake: When the CTU units arrive with the helicopter, they ask Teri to drop the weapon. She puts down the weapon, than it is a cut to a view from behind Teri and she still has the weapon in her hand, but is starting bend to put the weapon down.
Continuity mistake: In the scene where the CTU tactical team arrives at the 'lz', the chopper that first makes ground contact is marked "CTU-1", and offloads six federal agents in full tactical gear. Later in another shot of the same scene, you see "CTU-1" marked on a second chopper still circling in the air. It's clear this is not the same chopper as before, as we see the first "CTU-1" on the ground again moments later.
Audio problem: When Jack and Rick are talking in the water tower, a lot of the audio in that scene is either out of alignment or overdubbed. Easiest to spot is when Jack is checking Rick's wound. (00:10:30)
Answer: According to Jack in season 5, Nina was "deep cover" before the pair ever met, so it's safe to assume she was recruited before she joined CTU. As for what her primary mission was, who knows? Perhaps it was to gather sensitive intel and pass it on to her superiors. Given that she worked for an intelligence agency, it's not a stretch. Or perhaps we may find out in season seven.
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