Spoilers: "Critical Mass"
This doesn't mean anything. She certainly isn't looking at him like he's 'cute'. Amused - maybe. He tries to hold back the words he had saved for anyone who dared express an opinion other than sympathetic on his predicament. But he's rapidly losing recollection of them, all because she's looking at him like that. Head tilted one way, as if she's trying to figure him out, with a small quirk of a smile on her lips. Her lips parted slightly, showing the pink of her tongue, teeth biting it gently as she concentrates - on him. He definitely can't remember anything now.