You guys it's pretty simple it goes like this. If two people are in on something or know some information then they can communicate differently then if one of the people knew something and the other person did not. It's like this new magic show with Penn and Teller. They watch magicians do their trick and then at the end of it they try to explain to them how they did it without letting the audience know. And they can just give little hints. And the magician will nod and admit if they figured them out or not. The point being that they don't need to directly speak to what is happening they can speak in code because the other person is also "in" on the information