She's not surprised to see the shock on his face, but that doesn't mean it doesn't frighten her a bit. She watches him closely, reading his expression, the look in his eye, all things which speak to her as much as his words do. When he reminds her he can't have children, she chuckles under her breath, glancing aside and shaking her head.

"I know," she tells him, looking to him again. She remembers this conversation being had before, and she's well aware of how impossible this is, but then, impossible is what she's good at.

"No Immortal has ever had children.. with another human." She looks at him pointedly, because she's also told him that she's part Time Lord before, and her genetic make-up allows for a lot of advantages.