Is your pet a service animal?

The most used service animals are obviously dogs. Many of them are used for blind people. Yes, the most recent trait is to have dogs somehow detect serious illness in the owner before it get critical.

Besides dogs, I have seen monkeys being trained to serve people with disability. A monkey was trained so well that it will act like a maid and do everything short of cooking, then she would lock herself in a cage after everything was done.

I don't see how cats and parrots can be used as service animals. What do they do?