What's behind a pulse? The second episode dives into the world of an ice climber, a bus driver, a woman in labor, and a senior dance club to show how the human heart and the circulatory system power our physical and emotional lives, and create the pulsing rhythm of our world.

Will Smith discovers hidden worlds of fast and slow in the Earth's oldest desert. Worlds where things go so fast or so slow we don't even know they're happening. This hidden world of speed is everywhere, even 80 feet underwater. Hundreds of tiny anemones, anchored to the rocks, but film them patiently, then speed it up, and this miniature world comes to life. A lizard's tongue is one of the fastest movements in the entire animal kingdom. An orca creates a shock wave by slapping her tail and that pulse can travel through the water at more than a thousand miles an hour. to stuns the herrings she hunts.

An immersive cinematic experience of nonspeaking autistic people across the world, The Reason I Jump is based on a book written by Naoki Higashida when he was just 13. The film follows a young Japanese boy on a journey through an epic landscape. As a maelstrom of thoughts, feelings, impulses, and memories affects his every action, he gradually discovers what his autism means to him, how his perception of the world differs from others’, and why he acts the way he does—the reason he jumps.

The digital era gives rise to unprecedented opportunity to exploit, and be exploited. Troves of child pornography are available at the click of a mouse. Who are these children - and who profits from their abuse? While facilitating the darker side of our impulses, technology is also being touted as a cure to rehabilitate predators. In this episode meet the children who are forced to perform sex acts on camera; people who use the same technology to protect kids and nab the perpetrators; plus, a pedophile who reveals the roots of his addiction.

The human brain is the most complex object we’ve discovered in the universe, and every day much of its neural circuitry is taken up with the tens of thousands of decisions we need to make. ‘How do I decide?’ is a journey through the unseen world of decisions, and how they get made. Decisión-making is what allows us to navigate a course through life. Discover how important emotions are in making decissions and, as we learn more about our own brains, we can break away from slavery to our impulses. Neuroscience shows that you're made up of multiple competing drives and by understanding how choices battle it out in the brain, we can learn how to make better decisions.

The final episode of the series visits the frontline of the conflict with the world's top predators, meeting the scientists fighting to save them. Crossing five continents and combining landmark natural history footage with real-life human drama, it checks the pulse of the earth's iconic animals, including lions, tigers, polar bears and blue whales. With three-quarters of the planet's carnivores now in decline, can people find ways to live with predators before they disappear forever?