Day 3: 11:00 A.M.-12:00 P.M. - S3-E23
Revealing mistake: When Sherry is shot, the impact is visible on her shirt, but no gunshot wounds can be seen on her skin underneath, which can be seen as she falls to the ground.
Day 3: 11:00 A.M.-12:00 P.M. - S3-E23
Visible crew/equipment: When Julie is pointing her gun at Sherry, to her rear in the top right part of the screen there is a black shiny wall panel. On this panel you can see man's reflection, who appears to be wearing headphones. His reflection is in the shot for several seconds.
Day 3: 11:00 A.M.-12:00 P.M. - S3-E23
Continuity mistake: In the scene where Wayne and Fox are in Sherry's house searching for the pill container, right before Sherry asks, "What's going on here?" Wayne is seen wearing latex gloves. The camera then cuts to Sherry. When it cuts back to Wayne, his gloves have magically disappeared.
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.
Cubs Fan ★