Eames convinces Arthur that it would be really hot if Arthur had a dildo/buttplug/vibrator in him all day, and Arthur reluctantly agrees. Only to realise he's more sensitive than he thought. I would like Arthur really turned on but struggling not to show it, and biting his lip to maintain his usual appearance. Maybe he could squirm a little and blush too. And Eames is kind of an ass so, you know, he'd be making pointed remarks about the stick up Arthur's ass, or smacking Arthur on the ass or something. (If it is a vibrator maybe Eames could turn it on at random moments when Arthur is in the middle of SERIOUS WORK.) And maybe if Arthur lasts the whole day without taking it out he gets the reward of HOT SEX FROM EAMES.