When Disneyland first opened, it naturally attracted tourists with food and attractions. Of course, that same food and attractions also attracted mice. To keep the population of mice down (with the exception of Mickey and Minnie), Disneyland soon discovered feral cats had gotten into the park. Rather than capture and remove these feral cats, Disneyland decided to let them stay.
In return for staying at Disneyland (without paying for an admission ticket), the cats keep the mice population down. The next time you visit Disneyland, keep your eyes peeled for a stray cat roaming around the grounds. The cats often come out at night and even have their own Cats of Disneyland Twitter account where you can read the imaginary thoughts of Disneyland’s hidden but now famous cats.