Seth had always heard older co-workers complain about children growing up too fast. 'You are holding a baby in your arms one day, then you blink and the next day they are graduating high school'.
Of course, for them it was simply a morbid reminder about the passage of time and enjoying the youth of their children while it lasted. But for Seth it was a truly painful reality. He literally had his daughter age at a seriously concerning rate.
Thankfully, it seemed like she was steadying out. Her current age progression had actually taken less than a year and was in fact closer to 6 months, so it was even more concerning when it had happened.
But after Seth remembered the peculiarity of her birth, and Nixie's origins, he realised that he had seen this kind of ageing before. In Omelette.
