The book is full of examples of animal behaviour supporting the view that they are conscious, including their search for food, the relationship between predators and prey, the construction of artifacts and the use of tools, and the ways that animals communicate with each other. For instance, some birds simulate injury to draw predators away from their nest, and do so in such a way that it's hard to believe that this is just unconsious behaviour. There's also the caddis fly which builds a case for itself, and if this is damaged then it repairs it. Griffin argues that it is much more reasonable to think that it realises something is wrong and does what it needs to do to fix it than to postulate a mechanism whereby it responds unconsciously to specific stimuli.
It's a thought provoking book, but I felt that Griffin spent too much time worrying about behaviourism, which was rather out of favour when the book was written in 1984. It was an important challenge to those who would deny animal thought, but I'm tempted to search for more convincing arguments in more recent works.