Pleasurable Kingdom: Animals and the Nature of Feeling Good - Jonathan Balcombe
The big question in this book is whether animals (read: non-humans) know pleasure like we (read: humans) do. Balcombe states yes, although it's very hard to put facts to the statement. Because there are so few facts to base your opinion on, it is more the question whether you believe Balcombe or not. I did and I really enjoyed the book. I like to think non-human animals share many things with humans and for me Balcombe confirmed my thoughts.