 letting your cat outside with no supervision could cut their lifespan in half. That's because they face a lot of threats out in the world, like getting attacked by other cats or animals, getting hit by a car, or catching deadly diseases. Plus, cats are adorable little murderers. They kill about 2.4 billion birds a year in the US and they're linked to 63 different animal species going extinct. This doesn't mean that you can't ever let your cat outside, but if you do, always keep an eye on them. You could also build a patio for them. And if you have a fence yard, you can let them roam around under your supervision.