Identical twins Dr Chris and Dr Xand van Tulleken experiment and explore their way through the fascinating world of medicine and biology. The doctors show what really happens when you sneeze! Dr Chris gets his hands on a real human brain and Dr Xand goes on call with an emergency ambulance team. Meanwhile, over in accident and emergency, one patient has a hook caught in their hand and another thinks he's lost a toenail up his nose.

The doctors see how much pain they can take in their laboratory, Dr Xand investigates how our shoes can dramatically change the way we walk and Dr Chris goes on call with an emergency ambulance team. Meanwhile, over in accident and emergency, a patient comes in with a suspected hand fracture and another may lose his fingernail after trapping his finger in a car door.