At the end of episode "Our Mrs Reynolds" Captain Mal confronts Saffron for answers, ending with asking what her real name is.
To me it appears that she hesitates and he knocks her out. I can get why he wouldn't believe anything she might say, but I would have thought he'd listen to her lies. It would seem any information she might give could be a source to slip up.
Why doesn't he let her answer?
The shooting script makes it pretty clear that the pause is sufficient warning to him that she's preparing to tell another lie. He'd rather just not listen to it.
MAL : I got one question for you. Just one thing I'd like to know straight up.
SAFFRON : Ask me.
MAL : What's your real name?
She looks at him... looks away, considering the question... -- and he slams the butt of his gun into her chin, knocking her out cold.
He stands, regards her genuinely vulnerable form. Says with a kind of sadness:
MAL (cont'd) : You'd only've lied anyhow.
A beat, and he leaves.
