The substitution has to do with your gut feelings. It dramatically changes how you would deal with the situation, doesn't it.

We all (yes, I am included) will react to the cat as though it's "just another cat". The cat receives little more consideration than a broken signpost or blown down tree. There are members of our society assigned to take care of these things.

Now, if it were a HUMAN. That is different. This is a member of our own species! As a member, it is granted rights and consideration by us all and we all feel some obligation to it (more than to a cat or tree).

I sometimes feel this is a subtle form of discrimination. The cat is alive. Does it have rights? Do we get to exploit all living creatures who are non-human because we are human and they are not? The arguments of "superiority" due to ability to communicate or reason or feel pain are not valid because there are human members who will never be able to fulfill these requirements. Sure, I am aware of the "potential" argument (because they have the potential, they have full human status) but I believe some animals also demonstrate these qualities and have the same potential.

What would it be like for us to be captured and domesticated by a stronger race? What if we were lost and alone next to some alien roadway and couldn't find our care givers. When they domesticated us, shouldn't they have provided a save environment for us, protected us from things beyond our comprehesion?