Revealing mistake: We see a close up of the money in the truck and the $100 note has got "This bill is for motion picture use only" printed on it. (00:05:40)
Revealing mistake: Agent Lang takes a picture of a debit card inside the first victims car which is a clearly prop. The name is "Jane Doe", and the card number is 1234-5678-9101-1112. (00:05:40)
Revealing mistake: When Tony takes the book off Ziva, look at the cover. It's upside down. (00:10:20)
Lost & Found - S5-E9
Revealing mistake: The newspaper article on Lt Col Mann repeats the same few paragraphs throughout. Slow motion helps but is not required to spot this mistake. (00:12:20)
Revealing mistake: When Ducky opens the fridge and uncovers the body, the man's eyes twitch. (00:21:20)
Revealing mistake: In a close up of the iPod there is 1 song on the play list, playing at the 29 second mark. However, the icon to indicate that the iPod is on repeat is missing. Therefore, the iPod has only been playing for 29 seconds, despite the fact the crew left a good time before the team arrived. (00:07:20)
Revealing mistake: At the start, when the brain is being passed around you can see a fixed tube connecting to the student's arm to presumably pump the mercury into his hand. (00:01:20)
Cover Story - S4-E20
Revealing mistake: When Ducky is holding the dictaphone, it is off as the display is blank. (00:13:45)
Once a Hero - S4-E8
Revealing mistake: When we see Ziva having a close up look at the dead girl, the dead girl's eyes twitch and move slightly. (00:09:20)
Rendezvous - S14-E24
Revealing mistake: While McGee is bandaging what's left of Dean's arm you can see the arm is way to long to have the hand missing, you can tell the actor's hand is still there.
Untouchable - S3-E20
Revealing mistake: When the Lieutenant is explaining how her gun was in the victim's house, the camera pans behind Gibbs. Pay close attention and you can see a very faint shadow move across his back. Since we see there is nothing behind him on numerous occasions, it can only be part of the film crew. (00:18:20)
Untouchable - S3-E20
Revealing mistake: When Tony is winding the cat up in the carry basket, we see a side shot when the cat "attacks" him. However looking through the side of the cage, you can see the cat is nowhere in sight and therefore unable to attack Tony. (00:07:50)
Revealing mistake: Kate pulls the record up on the screen near the start and there is some writing on the file. This is a copy of the file she has in her hands. However the writing on the file as seen on the screen is Kate's next few lines. (00:09:30)
Chosen answer: It is never stated, however she must have been there several years if she is on presidential detail.