Book excerpt: Half of the world's population has one, the other half sometimes comes into contact with it, and yet a great deal of ignorance exists regarding the penis. Surprisingly many men think their penis is too short, even if it is above average in length. The fact that the morning erection is the last of eight nightly erections is a well-kept secret. Or that the foreskin, once unfolded, is as big as a postcard. Men always carry their penis with them, but they do not know it as well as they think. In this book, urologist Piet Hoebeke clarifies the mysteries of the male reproductive organ. Accessibly and humouristically written, Hoebeke explains the penis: Why do we have one? What does it do? How do I keep it fit and healthy? And of course: what to do when your foreskin gets stuck between the zipper of your pants?