Okay that gets a little wince. Eames has large hands, and it's definitely a stretch, but it's hidden while she's kissing Arthur. And really, kissing does more to distract her than Arthur playing between her legs. She could get lost in kissing. Being stimulated makes her want to seek more, makes her want to move. But now she's keeping nice and still for Eames, though that movement of his fingers is familiar enough, she will soon need to resist moving with it.