When at the airport where it shows all the agents Gibbs has lost throughout the years agent Brent Langer portrayed by Jonathan LaPaglia is missing from the group.
The 'S-Mine' referred to in this episode was a real anti-personnel mine manufactured in Germany and was the origin for the term 'Bouncing Betty' for it's method of detonation. However S-Mines have not been manufactured since 1945. Various countries have manufactured 'bounding mines' which have similar methods of operation however since the Ottawa Treaty of 1997 the manufacture of newer mines of this class has largely ceased.
In the final scene at the airport, when Gibbs sees all his deceased friends and co-workers, the first woman showed has been added digitally to the image and that is evident from the different lighting that falls on her.
When Luke is having breakfast at Gibbs' house, Gibbs tells him to put the milk in the fridge. When Luke doesn't move, Gibbs gets up, opens the fridge and says he won't ask again, leaving the fridge door open. In the next shot, as Luke gets up to comply, the fridge door is shut and Gibbs has to open it again.
After Abby asks DiNozzo and Bishop to read from her scripted report to Gibbs in her absence, Tony starts with saying "Gibbs" five times. Abby's script shows "Gibbs, Gibbs, Gibbs." instead of the 5 times as uttered by Tony. Tony is clearly seen "counting" the number of "Gibbs" with his head. Even Ellie does the same with her head.