It's a sentimental little gesture, that kiss pressed to his heart, and somehow Sherlock doesn't mind a bit. It's not the kind of thing he'd do himself, but the fact that it's Molly makes it pleasant, gives it meaning.

"Thank you," he says. And then, because it seems appropriate and because he's so drawn to the shape of her smiling mouth, he curls his hand around the back of her head and pulls her up towards him for another slow kiss.