Definitely focus your attention on the last chapter. There are many similes and metaphors used that depict Kino as an animal. Also, the setting helps this as well. They are in the mountains in a cave in the last chapter--a place where animals live. Also, it is said that animals go to that spot because there is water--it's their watering hole. Kino uses it in the same way that the animals do, for water and shelter.
I feel that Kino can be best compared to as an animal. I feel Steinbeck has used him to most to seem like he has adapted wild animal characteristics.
One specific example I know is the time Juana attempted to take the Pearl and throw it away. Juana could tell the unfortunate events that could/would happen from the greed of Kino because of the Pearl. When Kino awakens and sees Juana, he leaps onto her, snatches the Pearl, and hisses at her.