Here’s Where ‘NCIS’ Star Mark Harmon’s ‘Gibbs Head Slap’ Reportedly Came From

Anyone who has watched a few episodes of NCIS has most likely seen a moment in which Mark Harmon‘s character, Agent Leroy Jethro Gibbs, slaps the head of Special Agent Tony DiNozzo, who is played by Michael Weatherly.

The on-camera interaction has been going on since the first year of filming. In an interview with a French publication called Premiere, Harmon went into the story of how the slap originated between the two characters.

“Michael is a hugely talented actor, as is every member of this cast. My memory of when that happened, we were doing a scene. And he was on a Navy ship and he was talking to a female petty officer. I think this was in year one, early. And he was doing what he does, which is sometimes stay on script and sometimes not. I just reached over and smacked him. I tried to put him back on line. It was an instinct. It wasn’t thought, I didn’t think about it, I just did it.

To his credit, he stayed in the scene; he didn’t break. And I didn’t break. And the girl in the scene playing the petty officer, she was shocked, she was surprised. And she stayed there, and we just kept going. And people liked it. And every episode I was smacking him–maybe too much. We still do that occasionally, but sparingly. That’s where it came from.”

In a separate interview, Weatherly gave his take on the gesture, telling Festival de Television de Monte Carlo that he, too, recalls the first ever slap from Harmon back in the pilot season.

“I had a dialogue with an actor; maybe it was episode three or four, season one. And I was in the background and I didn’t have any dialogue. So, I was whispering to a girl was working in the background of the set. And all of a sudden, [Mark Harmon] came over and hit me on the back of the head. And everyone was shocked. And they printed it. The producers saw the footage. They laughed, because it was funny. Although it wasn’t really funny to anyone who was there that day because I was in trouble. And it just became part of the show.”

NCIS first aired on September 23, 2003. In its inception, the show was entitled, Navy NCIS, throughout the first season. Harmon’s character originally appeared in JAG for two episodes prior to NCIS.