She's watching him carefully, staying tuned into his movements and his sounds. Experimenting like this can be all kinds of overwhelming, and the last thing Joan wants is to push him too far. So when he arches his hips and pushes against her hand she smiles, glad that he's able to signal so clearly that he wants this.

She stays with her lips close to his, so close he can doubtless feel her breath, so that she's right there if he wants to kiss her. She gently strokes his anus with her fingers, just to get him a little more acclimated to the sensation.

Then, very carefully and very slowly, she begins to slide one finger inside.