Cats and dogs show fear, compassion, etc. Any creature which shows fear is aware of their own existence. YOU do not understand what sentience is. There are several articles relating to this subject, and it's generally accepted that Dogs/Cats are sentient beings.
Who is to say that the way they show fear doesn't manifest itself the same way mentally that it does in humans? If there are several articles relating to this subject, link me to them.
It's funny, because this article goes on displaying the rights of animals under the immediate assumption that animals are, in fact, sentient. http://en.wikipedia.org/wiki/Sentience#Animal_rights_and_sentience
All that says is that several countries recognize animals as sentient. That does not ensure that their philosophy is true. Learn to read.
Not that many people don't consider them to be. Again, an animal can experience fear, pain, compassion, etc. Your lack of comprehension towards this is pathetic.
I honestly don't think I'm going to be able to convince you that sentience isn't just the appearance of fear or pain, so I'm going to take a different route.
The main goal of any organism ever is to reproduce. In the case of dogs, they have 5 primary functions. Eat, drink, piss, stuff, reproduce. The most important of the 5 is 'Reproduce' which is pretty much the ultimate goal of every living thing on the planet. By killing a dog, you're depriving it of the opportunity to eat, drink, piss, stuff, and reproduce. Humans can do many more things than just eat, drink, piss, stuff, and reproduce. Our lifespans are also much longer than the lifespan of the average dog, which means murdering a human deprives them of many more years of life than just killing a dog.
Dogs are also not self aware, which means that they have no concept of, "self" or that they are a living thing. You can research more about self awareness by looking up mirror test results for animals.
Here's an explanation:
http://www.youtube.com/watch?feature=player_embedded&v=cTP01Wbsh0E#!