They get closer, and closer, then suddenly the bird flies up into the air. Often the cat doesn't even look up. To the cat, the bird simply vanished. Cats have been rated as the most intelligent animals under primates. Cats' brains weigh about one percent of their total body weight.
Human brains weight two percent of our total weight.
You would think that animals have no sense of disgust if you watch a cat who will sniff practically anything. But they can be disgusted. The cat will wrinkle its nose and leave the area, possibly displaying even more obvious signs of disgust in the process. There is one cat for approximately every four people in America. There is a very well-documented case of a kitten that climbed the Matterhorn.