On the bullet train back to Tokyo, I sat next to a Japanese woman who spoke English. We spent most of the trip talking about the places I'd visited and the things I'd experienced. Then I showed her a picture of the strange white fish part and asked her what it was. "Ah! Shirako!" she said. Then she said it was fish sperm. When I got to Tokyo and had an internet connection again, I googled "shirako," and read up on it. Shirako is the milt, or sperm sacs, of male cod. It's served in both raw and cooked form in restaurants all over Japan, but many Japanese consider it an acquired taste. The word "shirako" means "white children," and it is in season in the winter. It's also called kiku and tachi. It's kind of funny when I think about it. In my mind, caviar is appetizing, and caviar is the eggs of a female fish. But sperm sacs - the eggs of a male fish - doesn't work in my mind.