The book is not just about octopus and cuttlefish but about intelligence based on the evolution of our nervous systems. It seems the octupus developed their nervous system in a different way from mammals. And even between cephalopods seems to have evolved in more than one way.
Another things I was quite surprised is the life span of the octopus is around 2 years! There is a part of the book quite interesting about ageing. Why are there organism like sequoias that can live over 3000 years and then octopus with a very advance nervous systems only last 2? I need to re-read it again. As per my understanding this is related to the our evolution, we reap the benefits quickly but there is always drawbacks that turn up later.
There were parts were I didnt engage enough but I think it was worth it just for the two points above.