If you have a cat who spends time outdoors, consider bringing him inside instead. Cats kill about 3.7 billion birds and nearly 20 billion small mammals -- like rabbits and voles -- in the United States every year. Outdoor cats also live shorter lives. To transition your cat from an outdoor dweller to an indoor one, install several scratching posts and open cardboard boxes throughout the house. This will make indoor living less dull and slowly acclimate him to his new lifestyle.