Animals and Autistics seem to be a match made in heaven. Now, I'm not saying every Autistic is going to be like Temple Grandin and have her incredible ability to understand cows and other large animals. But animals don't pose the same things that cause problems when Autistics interact with humans. Animals couldn't care less if you remember to say "Hi, how are you?". Animals have their own rules, but they are a lot easier to figure out than humans! For example, my best friend is this hamster:
It's easy to figure out her mood. If she's chattering her teeth and ears are flat; she's upset. If she's got her ears up and is running around; she's happy. Eyes closed mean she's sleeping. There's no complicated hidden agenda, she'll never bully me, and the worse thing she can do is bite me. (which she usually doesn't)
I felt very proud to follow instructions on how to add onto her cage and was pleased at the end result (mainly because it made her happy!)
For me, she is also a bit of a sensory outlet. I love to watch her run around; especially spinning in her wheel. I like the little noises she makes and her wheel's steady noise. It's wonderful to pet her and hold her. (I'll give warning though, hamsters are not always pets that like to be held; Hammie just happens to be one that does)
So, I think animals can bring a lot of benefits to anybody with Autism, just consider the person carefully and do your research on what kind of animal you are considering. Also consider if the animal might scare somebody, because I know large dogs can scare me.