206 bones. One heart. Two eyes. Ten fingers. You may think you know what makes up a human. But it turns out our bodies are full of surprises. What makes tears of joy different from tears of sadness? Why is a gut feeling so much smarter than you think? And why is 90% of you not even human? You may think you know the human body – heart, lungs, brain and bones – but your body is full of extraordinary mysteries that science is only just beginning to understand. This book, which accompanies a major new BBC TV programme, will change the way we think about our bodies. Doctors are in the business of keeping secrets, but medical confidentiality isn't just about privacy, shame or discretion. It's about vulnerability to exploitation. In this ground-breaking new book, the effervescent van Tulleken twins bring their knowledge and charm to the page to reveal just how well our bodies keep secrets from the things that want to exploit it: bacteria, viruses, fungi, parasites, larger predators and, crucially, other people. They uncover the remarkable stories behind the science we are not meant to know, on matters of life and death. Leading us through these revelations are tales of everyday miracles – the human stories that bind every one of us together through the universal stages of life. From the most extreme environments on Earth to the most extreme events, Chris and Xand reveal the incredible abilities every human shares. Arranged around the three themes of learning, survival and growth, this book shows the human body like never before. Combining cutting-edge science and technology with stunning photography that gives us a tantalising glimpse beneath our skin, the van Tullekens reveal the secrets that make very ordinary human body ... extraordinary.