With additional reporting by Josh Horowitz
After MTV News put them to the test in a game of "Know Your Costar" -- a sort of Newlywed Game for actors-- at San Diego Comic-Con, the answer is... sometimes.
Sam and Caitriona couldn't identify each other's celebrity dopplegangers, and Caitriona was a little bit iffy on Sam's favorite sing-along-able song. But when the subject turned to on-set nudity? To quote Jaime Fraser, it would seem they know each other verra well indeed.