A newlywed sailor is informed by the Navy that he’s going to be drafted a long way from home on a remote island in the South Pacific for 2 years. A few weeks after he gets there he really starts to miss his new wife, so he writes her a letter.
"My darling," he writes, "it looks like we’re going to be apart for a very long time. Already I’m starting to miss you and we’re constantly surrounded by young, attractive native girls. The temptation’s terrible. I need some kind of hobby to keep my mind off them."
His wife sends him back a harmonica with a note reading, "Why don’t you learn to play this?"
Eventually his tour of duty comes to an end and he rushes back to his wife. "Darling" he says, "I can’t wait to get you into bed so that we can make passionate love!"
But she stops him with a wave of her hand. "First, let’s see how well you play that harmonica."