Mark Harmon, 60, has filmed more than 200 episodes of the CBS program "NCIS." In this interview with Jimmy Kimmel, Harmon demonstrates the famous "head slap," and explains how the move evolved (and how it's been haunting Michael Weatherly).
Previous to his NCIS stardom, Mark Harmon was known for his roles on popular television shows such as "Chicago Hope" and "St. Elsewhere," among numerous other TV and movie appearances over the course of over 30 years in the entertainment industry. He is one of the few actors in Hollywood to maintain a long relationship with a fellow actor as the husband of Pam Dawber.
Check out the video below for more from Mark Harmon, and to see "the slap" for yourself: