David McCallum Hated Mark Harmon's Infamous NCIS Pranks

Even on darkly serious shows, the cast needs to maintain some levity to break up the tension. That was the case on "NCIS," as Mark Harmon, who plays Special Agent Leroy Jethro Gibbs, was a notorious prankster on set. Brian Dietzen knew this all too well, as he told Looper about a painful prank Harmon played where he put a 40-pound sandbag in a medical examiner kit, making it much heavier than Dietzen anticipated. It's all in good fun, but Harmon knew there was one cast member not to be trifled with.

David McCallum was just as integral to the "NCIS" family as Harmon, appearing in 20 seasons before his passing on September 25. He played fan-favorite Ducky, and during a Reddit AMA, he answered numerous questions about his time on the procedural. Redditor u/scottheckman asked, "Has Mark Harmon ever played a practical joke on you? Since I have heard he is a major [jokester]." McCallum was spared from Harmon's antics: "Mark Harmon knows I am not the type to be toyed with."

While pranks are all in good fun, it appears Harmon didn't want to risk upsetting his co-star and friend. 

Mark Harmon left "NCIS" in Season 19, meaning he and David McCallum worked together for 19 years. That's a long time to get to know someone, and it seems they developed a genuine friendship. In an interview with Entertainment Tonight in 2019, later transcribed by the Man from UNCLE Canteen, Harmon said, "I'll always remember David McCallum. And I thought that from day one here, because I thought how fortunate this entire cast, whoever it is, is lucky enough to work with him and watch his work ethic every day. And take from his experience, what he's had in this industry, for a number of years, in different shows."

McCallum had acted for decades in dozens of projects, but it's safe to say modern audiences knew him most as Ducky on "NCIS." Following news of his death, many of his "NCIS" co-stars posted their condolences on social media. Harmon also released a statement to TV Line, detailing how much working with McCallum meant to him: "David lived a great, full, long life. I was in awe when I first met him and all of us on the show were honored to have toed a mark opposite him. My condolences go out to [McCallum's wife] Katherine and his family."

It's clear from these messages that McCallum's work impacted more than audiences. He touched the lives of all those who worked with him.