Cover Story - S4-E20
Continuity mistake: The way Ducky holds the dictaphone changes between shots. (00:13:45)
Cover Story - S4-E20
Continuity mistake: Just as Ducky is finishing reading the letter out loud to Gibbs, he has the letter in both hands. Camera cuts and now he is holding it in one hand. The Dictaphone also appears on the table instead of in his hand. (00:13:50)
Cover Story - S4-E20
Continuity mistake: When Todd is arrested, he has his hands behind his head. Camera cuts and now they are shoulder height. (00:28:00)
Cover Story - S4-E20
Continuity mistake: When McGee is free-writing, the stuff he has styped changes between the two close ups. While the words remain the same, the spelling and punctuation changes. "Was" becomes "Wsa", "Gat" becomes "gat", "desser" becomes "des" and "Bang" becomes "bang". (00:33:40)
Cover Story - S4-E20
Continuity mistake: When McGee is writing, we see he is working on a new paragraph. Camera cuts away for 6 seconds and then cuts back and now he is already halfway through the third line of that paragraph despite there not being enough time or enough pings of the typewriter resetting. (00:33:50)
Cover Story - S4-E20
Continuity mistake: We see Abby's phone lit up and ringing. Camera cuts and now it's no longer illuminated but still ringing. (00:37:00)
Answer: I hadn't seen the backdoor pilots yet but while it wasn't explicitly stated, at least onscreen, I heard somewhere Vivian got either fired from NCIS due to jeopardizing a case, got resigned from the agency, or transferred to the FBI.
Raykvega423