The tour was designed by Willie Williams, who has worked on every U2 tour since 1982. Williams had been toying with ideas for 360-degree stadium staging for U2 for a number of years, and presented sketches of a four-legged design to the group near the end of their Vertigo Tour in 2006. The inspiration for the 'spaceship-on-four-legs' design, nicknamed 'the Claw', came from the landmark Theme Building at Los Angeles International Airport.

This episode examines those birds whose sustenance comes from flesh and their methods of hunting. In New Zealand, Sir Attenborough observes Keas, parrots that do not eat meat exclusively, raiding a shearwater's burrow for a chick. However, it is the dedicated birds of prey, such as owls, buzzards, eagles, falcons and vultures, to which much of the programme is devoted. In order to spot and pursue their victims, senses of sight and hearing are very acute. Vultures are the exception, in that they eat what others have left, and once a carcass is found, so many birds descend on it that the carrion seems submerged beneath them. The Turkey Vulture is an anomaly within its group, as it also has a keen sense of smell. Eagles defend their territory vigorously, and a pair of sea eagles are shown engaging in an aerial battle. The Galápagos Hawk hunts Marine Iguanas, but can only do so when its quarry is vulnerable, during the breeding season. The African Harrier Hawk has adapted to extracting burrowing animals by virtue of an especially long, double-jointed pair of legs. By contrast, a shrike is not equipped with the requisite sharp beak and talons needed for butchery, and so dismembers its kill by impaling it on the thorns of acacias. The Lammergeier eats bones, and will drop them on to rocks from a great height in order to break them down to a digestible size. Also featured are the Eurasian Sparrowhawk, Goshawk and Peregrine Falcon.

1916. The war is raging in Europe and stretches from the trenches in France to the Italian Alps and the Balkans, and beyond to the gates of the Eastern world. The conflict becomes industrial, and millions of shells rain down on the battlefields; Verdun and the Somme are the deadliest battles in this second year of the war. Who can stop this infernal machine?

With a little imagination, could a few terrorists sabotage a mighty nation? Perhaps even tear down modern civilization? The stability of the US, Europe, China, or any global power depends on high-speed digital communication. Our increasing dependence on digital devices and global interactivity may be placing us in grave danger. Scientists around the world are dealing with new threats such as body hacking, Trojan horse viruses, and brain-damaging Internet addiction. But what if the ultimate threat isn’t an attack on technology, but the technology? Could the final superpower be the disembodied mind of the Internet itself?

The self-proclaimed 'Islamic State' is a jihadi militia active in the north and east of Syria, and in the west of Iraq, which has shocked the world with its cinematic staging of horrific acts of violence and its unexpected advances towards statehood. But why could IS expand so rapidly?

If you had less than one second to make a life-or-death decision to shoot a man who might be armed with a lethal weapon, what would you do? Would the ethnicity of the man affect your decision? Are you sure? The outcome – whatever your race – will surprise you. Brain imaging studies are showing that negative cultural stereotypes hijack everyone’s subconscious decision-making. But some science says we can overcome bigotry through exposure, self-awareness and flexible social networks… and, most controversially of all, ultra-violent video games!