Personally Ianto likes the feeling of Jack's hands on his arms, each tremor sending a little thrill of excitement through his body. He brings their lips together for another one of those sweet, languid kisses that contrasts so perfectly with the intensity of what they are doing right now. Only when he's sure Jack is utterly lost in it and melting against him does he hit that switch.
((I think my phone autocorrected 'rapidly' to 'tepidly' last time, haha! Awkward!))