Rarity made a humming sound of understanding and nodded. There was a lot of things that her friend did and spoke of that she could not comprehend. They did not have the same sort of technological advances at home for they had magic, which did many things for the ponies, and those that worked on engineering were simply not part of her world. Twilight was a genius in all styles but she was magical first and foremost. The idea of making a diaper filled with metal parts that took away waste was just beyond her.
Magic did that already. Of course, she didn't say this.
"So many children. That's so nice, to have such a large family."