The look Ianto shot back in Jack's direction was just as bemused and confused and other things ending in 'used'. He had no idea what was going on. Hell, he even shrugged. Jack's guess was as good as his.
Though, "What's this paradox you lot keep going on about? Is it like ... crossing timelines?" He knew only the barest bit about things like that. Just a mention, here or there, from Jack about how he nearly crossed his own timeline in the 40's. None of it made much sense. "And why do you lot seem to be waiting for something to happen?" Both Rose and Jack both looked like they were waiting for Death to show up (again) and start knocking heads together or something.
Ianto tucked away the scanner and went to rejoin the group, just in time to hear one of the Doctors go on about suits. He adjusted the knot on his tie, smoothed out his waistcoat and said, "Every girl's crazy about a sharp dressed man."