Ruby holds her breath when she comes.
Sam can feel her body quiver, hear her soft gasp, but then she screws her eyes shut and doesn't make another sound. He wishes that she'd moan or say his name, or even make those fake porn noises, anything to make her more like all the other girls he's fucked.
That's how he used to keep himself sane, by thinking she's just another girl, someone to keep him warm instead of cold and alone. Now her silence makes him wonder and think, wishing for things he has no business wanting from a demon.