You never know when Japanese customs will catch you off guard. When our kids were born, I insisted on being in the operating room during the birth so I could be the one to cut the umbilical cords and help bring them into the world. This was rare enough that I got some surprised comments from the doctor and nurses, who were impressed with my dedication. I was talking about this event with my wife one day, and she told me "Oh yes, and I still have those umbilical cords saved in a drawer." Supposedly, it's considered a requirement for parents to save that all-important memento of their children when they're born, to dry it and put it in a specially decorated box and keep it safe. Another interesting child-related custom is that of throwing baby teeth that have fallen out either on the roof or under the house, depending on whether the tooth that came out was on the bottom or the top of the mouth, respectively. This ensures that strong teeth will grow in the future.
Oh look, honey, I found an old box in a drawer, I'll just open it and OH MY GOD!