In the fifth episode of "Superquark," the journey into the game of seduction continues with BBC documentaries, revealing which animal species manage to survive despite having extremely slim chances of success in courtship: some must seek a partner where finding one is almost impossible, others must adapt to a world completely different from that of their parents, or to reproduce, they have developed some of nature's most extraordinary strategies. We then delve deeper into the thyroid, a small but vital gland whose properties are well understood, but its true self-regulation mechanisms are less so. An all-Italian project is now underway to discover how it works. Barbara Bernardini's report uncovers the thyroid's "black box." A new technique will reveal how hormones are actually produced.