Why do you think Grandin prefers animals to people?

Temple Grandin prefers animals to people because she can relate to them more easily. Temple has autism, a neurological disorder that essentially makes people with the condition live in a world of their own. People with autism like Temple think visually; this is one aspect of their condition that gives them an often greater degree of empathy with animals than with other human beings. Animals lack the power of speech, so naturally their thoughts are also visible.
From these images in her mind, Temple constructs associations—something she notices is common among animals, for instance in horses. These associations are important in that they are highly determinative of animal behavior. For example, if a rat is shocked on entering a passageway in a maze, it will associate that experience with fear and so will never go back there again. Fear and associative thinking also combine in autism. People with the condition tend to see the outside world as an intensely hostile, dangerous place. They see themselves almost as prey in much the same way that animals do.
These insights allow Temple to devise a humane method of slaughtering cattle on farms and in processing plants. The whole procedure of slaughter can be made more efficient and less frightening for the cows if their fear and capacity for associative thinking can be taken into consideration.