"You'd think being used came naturally to you." He's not sure he's saying it only to Kaz, not sure if it really is just banter. They're using each other a little and letting themselves be used. It's how they cope with pain in their worlds.

He circles Kaz with a third finger ready to slide in. Rat is slim enough that Kaz might be all right with the stretch of two fingers but three will make it good.