Since it hit the airwaves in 2003, NCIS has become one of America's favorite shows, and we're still tuning in each week 15 seasons later.
If you keep an eye out, you might notice sneaky references and hidden jokes in certain episodes. NCIS super-fans have picked up on lots of clever bits of trivia that you probably missed. Here are 11 of our favorites:
1. Cote de Pablo needed a Hebrew tutor
While she plays the Israeli Mossad agent Ziva David on the show, de Pablo is actually a Chilean-America. Whenever Ziva spoke Hebrew, she had to depend on her language tutor to help get it right. But de Pablo has her own talents. She did all her own stunts, and also used her own voice whenever Ziva sang in an episode.
2. Most Wanted
Keep an eye on the Most Wanted board in the NCIS office. Throughout the different seasons of the show, the faces on it change. Actual bad guys from the show are included, but so is Osama Bin Laden - whose photo was crossed through with a big red line after he died.
But eagle-eyed fans will notice agent G. Callen from NCIS: LA and series creator Donald P. Bellisario on the board in certain episodes. Pretty sneaky.
3. The fade to black and white
Here's a tricky trivia question that will stump even the most devoted NCIS fans: what is the noise we hear when the show goes to commercial? Some say it sounds like a camera shutter clicking, but it's not.
The sound was actually made by Donald P. Bellissario hitting a microphone with his hand. He needed something recognizable and dramatic for the sound, and decided to take matters into his own hands.
4. Abby is based on Pauley Perrette
Producers for NCIS admit that fan-favorite character Abby was heavily inspired by Pauley Perrette, the actress who plays her. Perrette has a college degree in forensics and a masters in criminology. Like her character, she was born in New Orleans, and when we see a photo of Abby's adoptive mother on the show, it's just a picture of Perrette's actual mom.
The one big difference between them is that Perrette is actually blonde. She once had an allergic reaction to her black hair die, which sent her to the emergency room after her face swelled up to twice its size.
5. What exactly is a Caf-Pow?
Abby's energy drink of choice isn't real, sadly, but you can buy Caf-Pow merchandise. For the authentic NCIS experience, fill your mug with Hawaiian Punch. That's the drink that was used until Perrette cut sugar out of her diet, and the show switched to using unsweetened cranberry juice instead.