[Jamie, you're the first person ever to give a retort to his silly "what kind of butler..." catchphrase. For a second his expression even turns mildly surprised that she did. It melts back into his usual cool smile soon enough, although he sounds entirely sincere in his answer, as is appropriate when discussing something as serious as a butler's aesthetics:]
Oh, that will not be a concern. As long as my master needs me, I will not be rendered incapable of serving him. [So it follows that he can throw himself into any kind of mortal danger without risk? Sebastian's logic: equal parts confident, stubborn and plain circular.]
[When he first entered his contract with Ciel he thought being forbidden to lie was an annoyance. These days he mostly considers it a fun challenge to work around it. Right in this moment, it's a bit of both. She's obviously clever - would she even fall for distractions or carefully chosen words? ...Well, why not test that?]
Ah, you did? [The implication that she did a little more than just look isn't lost on him, of course, so:] It must have been an experience?
[And he clasps his hands neatly behind his back, looks at her with faintly raised eyebrows - all interest in hearing her exciting story. Let's talk about her and not him. Oh, he doubts she'll bite, but...]