Interesting fact:

Remember the hit TV show "Gilligan’s Island"? According to a 1994 audio book co-authored by Russell Johnson, who played “The Professor," the show’s pilot episode finished filming the same day President Kennedy was assassinated in Texas. This is why during the opening sequence of the series the U.S. flag can be seen flying at half-staff. Eagle-eyed viewers will notice this is only in first-season episodes.