[Under normal circumstances, someone doing something like that wouldn't necessarily cause him to blush, but it would at least get him to grin and start flirting back]
[... like this, though, because it's Constance of all people, and he has it planted so firmly in his mind that 1) she's a friend and 2) she and d'Artagnan are in love, he's left looking somewhat bewildered as he pulls back to look at her -- smiling, but perhaps a bit hesitant and very ???]