[Ain doesn't have normal reactions to things, and like. he's been there. So all he does is laugh quietly, sitting up a bit to give Vash a warm, pleased look.]

Did that feel good? [He asks, knowingly, making some happy clicking noise in the back of his throat on instinct.] Don't worry, I'm alright. You didn't do any damage with that. I thought it was cute!

[He is very, very casual about all of this, partly because Ain has the general demeanour of someone who is never worried (he is always worried but that's not the point), and partly because he doesn't want to say something gravely serious and freak Vash out. If getting kneed in the ribs leaves a bruise, oh well, he'll live.

He's also not sure how to explain the technical anatomy here, and maybe a discussion on science is not sexy in bed. Ain doesn't know. Ain can barely function as it is. He'll just save the anatomical names for later, he thinks.]

Do you want me to continue? You're doing well! I'm impressed!