In one scene Ducky refers to the Bertram Mills Circus, which existed in the real world in England from 1920 until 1967. It became especially well known for its annual Christmas shows, which members of the royal family, Winston Churchill, and UK and foreign dignitaries routinely attended.
During the episode, Tony is interested in (and McGee briefly dates) an Agent Tina Larson. Her last name is most likely a joking reference to Glen A. Larson, the creator of the original Battlestar Galactica (1978), a series upon which NCIS (2003) co-creator Donald P. Bellisario wrote for and produced earlier in his career.
Gibbs smacks his own head in the elevator.
When Gibbs first met William Danforth, Sr., the victim's father, he said that "AFIS couldn't match the body in autopsy with Lance Corporal Danforth's DNA". However, AFIS (Automated Fingerprint Identification System) is a database of fingerprints, not DNA. A separate DNA database exist, the most commonly used in USA being the FBI database, CODIS (Combined DNA Index System).
Corporal Merrill mentions eating out at a restaurant named The Gold Monkey. Tales of the Gold Monkey (1982) was a short lived TV series produced by Donald P. Bellisario and Belisarius Productions.