She wasn't smiling anymore, but the look in her eyes was doing the smiling for her.
Sometimes it was really helpful not to be human. Phaedra had meant that Peter should understand that she was capable of getting at most of what was in his head. So when he kissed her head and swam away, she shook her head, then ducked herself under the water and followed him.
Once she'd caught up to Peter, she intentionally slid past him, skin brushing against his, before putting her feet down and standing.