Your words might be sincere, but your smile is false.
That makes no sense to me. If her words are sincere then her smile which should be related to the topic at hand, should also be sincere. Unless she's actually thinking about something other than the topic at hand, and that's whats making her smile fake. .. huh.
But then there's the word "might". Maybe Sai is having a hard time reading Sakura.
The trailing periods after her speech give the impression of her statement being "in the air". So it does look like she's holding something (probably Sasuke related) back.
This.
To me, Sai doesn't want to believe Sakura is lying. Because she's his friend, he trust her words by default.
I think that's why he assumed she wasn't lying. Moreover, he said "might" ( i would like to have the raw's translation by someone who understand japanese ). But it's clear to him that her smile is fake. And it's clear that she's lying.
I liked the chapter. I knew it would be something like that beteween Tsunade and Orochimaru.
But i don't really like the fact that Sakura is still hurt that much about Sasuke being an ass.
I honestly though she would react differently.
To me, this isn't kill more SasuSaku. It's quite the opposite in my opinion. It will let a window for Kishimoto to say later that Sakura was super-sad because she loves him so much bleh bleh.......