No matter who you are, you've probably seen an episode of NCIS. But whether you're a casual fan or a die-hard lover of the crime show, you might not know some of the behind-the-scenes trivia throughout the years. The fan-favorite series debuted in 2003, and doesn't appear to be going anywhere anytime soon. Here are six facts you probably never knew about NCIS.


1. The Original Title


Originally, the show was going to be titled: NCIS: Naval Criminal Investigative Service. Although it would've been redundant to spell out what the acronym stands for, it was believed it could sell better if people knew what exactly the letters meant. It's definitely catchier now.


2. Gibbs' Flashback Scenes


Sweetly enough, when Gibbs is shown in flashback scenes, he's actually played by the actor Mark Harmon's son, Sean Harmon.


3. Pauley Perrette's Background


Pauley Perrette, who plays the loveable Abby Sciuto in the series, actually has a scientific background from before she pursued acting. Reportedly, she has a Masters in criminology and sociology. The actress even went on to create a forensics scholarship in honor of her NCIS character.


4. The Family Ties


Co-creator Donald P. Bellisario included his family in the show, as his stepson Sean Murray plays Timothy McGee, and his daughter Troian Bellisario plays Sarah McGee. Bellisario's son, Michael Bellisario, plays Charles "Chip" Stirling, and even his wife Vivienne had a role, playing Gibbs' mysterious redhead love interest.


5. Auditions


Lauren Holly, who is credited for playing Jenny Shepard from 2005 to 2015 (some through flashbacks), reportedly originally auditioned for the role of Caitlin "Kate" Todd, which went to Sasha Alexander.


6. Mark Harmon's Role


Reportedly, Donald P. Bellisario was not sold on casting Mark Harmon for the leading role as Gibbs. However, once he saw the actor play Simon Donovan on The West Wing, he decided to give him a chance.