Although not all of the studies are complete and some have not yet been peer reviewed, they show what anyone who has spent time with animals already knows. From ants to elephants, there is a level of intelligence. What we sometimes thought was anthropomorphization was actually a hint at what lies in the animal mind.
Written in a way that makes the studies easy to understand while also entertaining, I recommend Animal Wise if you have ever wondered what animals are thinking.
P.S. I made a Pinterest board of my favorite facts from each chapter here.