Why do you think a cat purrs? I think it is because, you know when you feel happy, nervous, or anxious? You breathe deeply. Sometimes you might hear a rumble in your throat. Maybe, when a cat purrs, its mouth is closed, and the breathing has a disruption when it gets to the lungs and voice box. So, when the cat breathes out, the "purr" comes. Reply if you agree! If you have a different opinion, write it down in the comments below!