Now, I am going to throw all the scientific stuff aside. I have introduced six cats to one another, not counting my mom's cats. I have had very little problem. I do a slow introduction, with the new cat in a room by itself. By the tenth or so day, things are just fine.

I don't pay any attention to how they act, how they cower, what they look like, how they react with their paws, etc. I think animals react to one another than they do to people. So, a cat that cowers at the shelter may be the opposite at home. I have four fairly outgoing cats, two timid girls, one alpha alpha male (he is one of the outgoing ones), and there is a distinct pecking order. For me, it just all worked out.