The experts dissect a lion and a tiger and travel to South Africa to see lions in the wild. From the outside, the lion and the tiger look very different, but once their skins are removed, even the experts find it hard to tell them apart. At a big cat rescue centre, biologist Simon Watt traces the evolutionary history of the feline family, and comes face to face with a liger: a cross between a lion and a tiger and proof of how similar the two species are. One of the most characteristic features of these magnificent animals – and something that distinguishes them from the small cats – is their ability to roar. It's something that has intrigued scientists, so the team delve into the lion's throat to find the voicebox, and make a discovery that helps explain the way the vocal apparatus works like a trombone. The team dissect the anatomy of how these deadly machines work, from the big cats' powerful forearms and retractable claws, to the powerful killing bite. Richard Dawkins explains the evolutionary arms race that has arisen between predators and their prey in the struggle to survive. And the experts try to find out why male lions have their distinctive mane of fur.