He placed his hand over his heart, eyebrows raised in mock offence that she wouldn't believe him.

"Swear to god, it was at least sixty percent chocolate-tasting."

What he's trying to do is get her mind of it, and get her to smile, maybe even laugh. Maybe he's doing it for himself, too, as if getting her to relax will make him worry less about the fact that maybe she's going to die, tonight.

There was nothing they could do to fix it - better to pretend he wasn't worried about it.