1. What is a vaccine and herd immunity?
2. Programs from series

The doctors take on their smelliest investigation yet when they find out how the shape, size and pong of your poo can tell you a lot about your health! And Dr Xand donates blood to see how it is processed to help save lives.

Dr Chris swallows a super cool camera pill to follow the journey that food makes through his body. And Dr Xand explains how strong our bones are and meets someone who has developed the technology to grow bones!

The doctors investigate what happens when blood is full of oxygen by whisking up a blood smoothie. Dr Xand visits a special medical collection of body parts to find out some ways in which human organs can go seriously wrong.

The doctors perform an experiment with wee to explain what it is made of and why our bodies produce it. And Dr Chris comes face to face with 180 of the world's most dangerous snakes!

Dr Chris inserts a tiny medical camera up his nose and down his throat to look at how our vocal chords work, and takes a terrifying ride on a super-scary roller-coaster to find out how our bodies deal with fear.

Dr Chris takes a terrifying, stomach-turning ride in an aerobatic display plane to explain what happens to your body when you feel travel sick. Also the doctors put on their PJs to investigate all about sleep.

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.

The doctors demonstrate how our body movements are controlled, by confusing their very own brains! Dr Chris lets a blood-sucking leech feed on his arm and Dr Xand goes on call with an emergency ambulance team.

Dr Chris and Dr Xand turn back the clock and look at what medicine was like in the First World War. They meet a Paralympian runner who swaps her blade for a Great War leather leg, look at the small creatures that infested the trenches and set up an experiment to demonstrate how soldiers' bodies coped with the pressures exerted by huge explosions.

Dr Chris inserts a special medical tube into Dr Xand's nose and down to his belly to prove that our nose, mouth and stomach are all connected!

The doctors show you 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.

Operation Ouch is packed with incredible facts about the human body and the fascinating world of medicine and biology. Today, the doctors experiment on their muscles to show they work! Dr Chris meets some wriggly maggots that are helping to heal a sore foot and Dr Xand goes on call with an emergency ambulance team.