"Doctor?" asked Sarah. "What's it like to have two hearts?"
"Hmm?" The Doctor looked up from the TARDIS console. "That's an odd question. Why do you ask?"
Sarah shrugged. "Just curious. Tell me. What's it like?"
The Doctor pushed his hat back from his face and regarded her. "What's it like to have one heart?"
Sarah laughed. "Normal."
"Exactly." The Doctor pulled his hat back down, then returned to the console. "You humans ask the silliest questions."
"Oy," protested Sarah, following him. "Don't you get all superior on me. I've seen you ask far sillier questions."
"Nonsense," said the Doctor. "Only a human would demand to know what it's like to not be human."
Sarah gave an annoyed tug on his scarf, then placed her hands on his chest to feel the double heartbeat within. "You can't blame me for wondering, though. Sometimes you act very human."
"And sometimes," said the Doctor, "you act very Time Lord."
"I know," said Sarah. "I ask silly questions, don't I?"