The doctors explain how we breathe by inflating a real pig's lung, and Xand finds out all about the biological changes that happen when you hold your breath. Dr Chris gets icky and picky as he takes a very close look at the job that snot, bogies and mucus do in our bodies. And there's no need to be scared of scars as we find out how your skin heals itself after an injury. Meanwhile, over in accident and emergency, one patient is rushed in with a worrying eye injury after a dangerous accident with a pellet gun, and the trauma team is on standby as another comes into hospital with a potentially serious head injury.