Most Americans think of cats as pets. But not all cats are pets. Some cats help people and other are a problem. For example, on farms and in old house, cats can help. They kill small animals such as rats or mice. But sometimes, people do not want cats around. Some people like to watch birds in their yards. Cats may kill the birds or scare them away. Cats are also a problem in cities. In Rome, for example, thousands of cats live in the streets and old buildings. They make a lot of noise, and they are dirty and dangerous.