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.

Professor Brian Cox takes on the story of the force that sculpts the entire universe - gravity. Gravity seems so familiar, and yet it is one of the strangest and most surprising forces in the universe. Starting with a zero gravity flight, Brian experiences the feeling of total weightlessness, and considers how much of an effect gravity has had on the world around us. But gravity also acts over much greater distances. It is the great orchestrator of the cosmos. It dictates our orbit around the sun, our relationship with the other planets in our solar system, and even the way in which our solar system orbits our galaxy. Yet the paradox of gravity is that it is actually a relatively weak force. Brian takes a face distorting trip in a centrifuge to explain how it is that gravity achieves its great power, before looking at the role it plays in one of the most extraordinary phenomena in the universe - a neutron star. Although it is just a few kilometres across, it is so dense that its gravity is 100, 000 million times as strong as on Earth. Over the centuries our quest to understand gravity has allowed us to understand some of the true wonders of the universe, and Brian reveals that it is scientists' continuing search for answers that inspires his own sense of wonder.

We all agree lying is shameful. Yet we still deliberately deceive each other constantly. Are our brains wired for lying from a young age? The brains of pathological liars may provide insights. Will technology make it easier for us to be dishonest, or could it someday instantly reveal someone is lying? Perhaps we are deceitful because our limited senses prevent us from seeing the real truth. Scientists say our own memories deceive us, and have managed to implant false memories. Other scientists look for ultimate truth in the subatomic world … only to end up turning reality on its head.

The determination of the German forces to keep on fighting in the face of defeat had disastrous consequences. After the Allied landings in the summer of 1944, the Wehrmacht was on the defensive on all fronts. It was clear to the German generals interned at Trent Park that Germany would soon lose the war. In mid-1944, Gerhard Graf von Schwerin chose to use common sense instead of blindly obeying Hitler's orders. He decided to surrender the city of Aachen to the US army to avoid bloodshed. Other commanders such as Field Marshal Ferdinand Schorner kept on pushing their soldiers to give their all. Despite being outnumbered by the Soviet forces, Schorner forced his soldiers to hold out in Sworbe, a 200 square kilometre peninsula on the coast of Estonia. Thousands of soldiers died. Yet Schorner's attitude and the urging by Hitler and Goebbels to hold out were accepted by a large number of young soldiers. By April 1944, the Ruhr pocket was completely surrounded, yet Field Marshal Model refused to surrender, so that 1.2 million German soldiers and a large number of Allied soldiers died between January and May 1945.

There is a strange and mysterious world that surrounds us, a world largely hidden from our senses. The quest to explain the true nature of reality is one of the great scientific detective stories. Clues have been pieced together from deep within the atom, from the event horizon of black holes, and from the far reaches of the cosmos. It may be that we are part of a cosmic hologram, projected from the edge of the universe. Or that we exist in an infinity of parallel worlds. Your reality may never look quite the same again.

Horizon explores the strange and wonderful world of illusions – and reveals the tricks they play on our senses and why they fool us. We show how easy it is to trick your sense of taste by changing the colours of food and drink, explain how what you see can change what you hear, and see just how unreliable our sense of colour can be. But all this trickery has a serious purpose. It’s helping scientists to create a new understanding of how our senses work – not as individual senses, but connected together. It holds the intriguing possibility that one sense could be mapped into another.