"That makes two of us," came the Doctor's reply, opening his eyes wide and raising his eyebrows in a comical way. Jemma's excitement was addicting. It was one of the reasons why he liked to take new Companions, despite the heartbreak of eventually seeing them leave: their reactions and observations were refreshing, letting him experience the wonder of the universe through their eyes when it was so easy to take things for granted. And while he didn't necessarily consider Jemma a companion yet, he could still get that treasured reaction from her.
The Doctor turned to lead Jemma to the TARDIS, but when he reached the door, he looked over his shoulder at her and said, "Be careful of what you say. She can hear you." He placed his hand upon the door frame and looked lovingly upon her. "What you see is not her real form. She disguises herself with walls and floors and whatnot, but she's an organic entity. The hum you hear when she's resting is her breathing. Taking about reverse engineering her would be like me asking to perform a living autopsy on you."