Most wildlife documentaries focus on animal behavior, but INSIDE NATURE'S GIANTS goes inside the largest animals on the planet to explore their anatomy, reveal their intricate inner workings and uncover their evolutionary secrets. In this episode, veterinary scientist Mark Evans and comparative anatomist Joy Reidenberg dissect a lion and tiger at the Royal Veterinary College in the UK. On the outside, the lion and the tiger look very different; but once their skins are removed, even the experts find it hard to distinguish the two. One of the first questions they tackle is the anatomy of the roar-a characteristics that separates big cats from small. Then they move on to the big cats' powerful forearms, protractile claws, and powerful killing bite.