That broke his stride (unfortunately, frustratingly--and he'd been getting into it too). But only for a moment. Just use it as a pause, a moment of slowness.

"Now why..." he whisptered, "...would I ever do something like that?"

He could think of several good reasons, actually. But, no, this was an encounter to be kept between them, to be thought on by both involved, and for the secret third to be kept ignorant of--because that would make the whole thing better.

"I won't. I promise."