The look from Jack was caught, curt nod and all. If the Doctor ever had a cryptic expression he was not using it now. Instead, Jack encountered a rather stern faced man who's look said quite plainly 'bad idea.'
The Doctor nodded to Logan; and while he didn't quite want to admit that he thought Logan a bit more of a barbarian than Jack - it did suprise him that he would have come out for something like this. Really, who does this?
Keeping his distance he continued to chew on his apple hoping it would become a battle of words rather than physical one-up-manship.