I remember this being explained to me as being a reference to the political body…and it was never clear to me if both bodies were the political body or just one. But now, I’ve gone ahead and looked this up and it sounds like this is a “well known saying” of the time. Maybe it’s a little like saying, “You have a right to remain silent” in our culture – a recognizable official thing to say. It highlights Hamlet the clown but it’s also Hamlet the verbal wit. He’ll draw on anything to make his point.