It was difficult to write, in some places. It's not just the torture, it's the mind games that really get Jack. For me, it was interesting writing Jack being tortured, because he's admitted he once was a torturer himself. So does he know what's coming? What's he thinking of? I suspect he'd be thinking of his own previous victims, trying to figure out what the Master's doing to him. And some part of him does realise that he's trading one captor for another (when he turns to Ianto), but even knowing the psychological trap he's falling into, he can't bring himself to care.

That's the fun thing about Jack. He knows what he's getting himself into, but... he lets himself fall anyway. And so the consequences of that are even more interesting than if he didn't know what was happening.