She smiled at him as if they had some private joke going between them.
It was something of a private joke between him and the general.
She smiled as if he'd told her a private joke.
We had 10 years of private jokes and a word can just send us.
It was, even at its beginning, a happy private joke between two wise women.
The thing was just a private joke between my wife and me.
The message had to be a private joke, since no one else could have been expected to find it.
He chuckled a little, as if at a small private joke.
Or maybe he was just amused at some private joke of his own.
Rather, he seemed to include her in some private joke that only she would appreciate.