Martha Knew!

I've seen this movie a zillion times and somehow missed this; Martha is dusting the picture of Lucy in her bathing suit, and she looked disgusted. Then she moves to the Captain's portrait, and she looks exactly like she's hearing him make a cutting remark. This marvelous smirk flits across her face! Also. The way she started using seaman's terms out of nowhere- shipshape in Bristol fashion- was another clue I missed.