The father of YouTube cats Porky Belly and Jim, has tested his cats' ability to resist knocking things over, using the laws of cat physics, which dictate that if an object is at rest at the edge of a table, it must be knocked down. The video shows a paper towel roll being pushed over, a bottle of painkillers, and a USB flash drive. The tests proved successful. The urge to push items off edges is often attributed to cats' hunting instincts and their curious paws reveal a lot of information about the world around them. If your cat is persistently pushing things off edges, it may be a sign of boredom.