The second episode of this unique scientific study reveals the wild side of pet cats. Using GPS trackers and cat cameras, they show how these felines transform from pampered pet to purring predator as soon as they leave the cat flap. Liz Bonnin and some of the world's top cat experts put Ozzy and Smudge under surveillance to find out who is king of the street and reveal why, no matter how hard we try, we can't keep our cats' hunting instincts under control.