http://www.keepmyfile.com/image/f6c08c1488980
Here is the still of Jack right before he says the now-famous (or infamous?) "keep telling yourself that" line. The link doesn't have great stills of Liz and like someone said, she just looks tired, and she should be tired! How much has the girl been through up to this point and she's probably just been called out on killing Jack. She's not in the mood to flirt, but she's not being completely honest with him, either, and he can see right through that. Look at his eyes there. There's no real anger at her anymore. I think he's over that, just a little hurt.