There was something in River's eyes that caught the Doctor a little off guard- even more than usual. Something in those eyes that didn't quite feel right. And then, she kissed her and... no more spoilers.
Her hearts were racing. She felt her mouth go dry. She'd had issues with this bloody togue since the start, but now...oh, how she wished it could wet itself because she was speechless. And that was scary enough for the Doctor, wasn't it?
"Oh," she whispered back, staring at her. She was gone, but here? It quickly dawned on the Doctor that this was not the first person she'd met back from the dead. And now, the wheels were turning.
"You...so, you've been to the library. Right. Okay. And it worked, right? The sonic?"