[She anticipates the question. After all, the Doctor has needled her enough for being "Earth-centric" during their travels; she doesn't want to offend anyone, least of all River.

(She also doesn't want to come across as anything less than razor sharp and extraordinarily intelligent).]

See enough planets, meet enough people, and you start to realize how to tell the difference. It's in the details. The contents of the first aid kids, the equipment in the gym, the coffee cup left in the control room - they might not be exclusively human needs, but they all add up to someone with a hell of a lot of biological similarities.