He was making her tongue-tied, at a complete loss for words. He'd always done this to her, Superman at least, and now she was trying to figure out how to respond. With Clark it was easy to respond, with Superman, and the way he looked at her, it was much more difficult.
She fought a blush and ducked her head for a minute, still smiling happily to herself.
"I'm still trying to take all this in," she explained. The smile was replaced by a more serious look. "You gave up your powers... for me." Lois had been wanting to talk about that.