Beginning at 40:46, when Parker is taking to his friend Billy Doyle, and ending at 41:38 when Parker leaves, the pull chain on the lamp on the desk moves from side to side. Begins with the chain on the left where it belongs to the right where it doesn't and back again.
Everyone keeps repeating that the victim was studying "possums." The educated NCIS agents would surely know that "opossums" is the correct word. There are no possums in the U.S.; only the Virginia opossum lives in the U.S.A.
Nick tells the woman in the bar he will show her his badge.
A badge is worn on clothing. The proper term for the ID he shows her is 'credentials'.
Palmer said that the two bullet holes on front of the victim's chest were exit wounds and that there was one more on her back, from a bullet that didn't pass through. Surely, there should have been *three* more on her back, including the entry wounds for the first two.
In the period of a few days, based on Knight saying she needs a date for her cousin's wedding, the team, together or individually, travels back and forth several times to Philadelphia to work on the case. Not much time appears to pass getting from one place to the other.
McGee gives details of a crime from Hanna's rap sheet. Knight then says "That's nothing. You should see her rap sheet." They both had copies in their hands and McGee was reading from his.
McGee says "It'll be date night for Delilah and I." That should be "for Delilah and me." McGee makes this grammatical error regularly. It is hard to tell whether this is poor English from the scriptwriters or a deliberate attempt to highlight McGee's pretentiousness. (Many people say 'I' when they should say 'me' in a misguided effort to sound posh and/or educated.)