Taz feels like one of my kids, and for the most part, she acts like she's one. (except she's seems to be better at doing as she's told!)
She can't talk like the rest of us, but she's got some VERY distinct facial expressions (like the one I've show here.. its her "Mom, I need to know you still love me even though I just got into trouble face.")
We've discovered that its her ears in particular that convey so much of what she's feeling, she's very comical and endearing when she's unsure which expression to use, her ears move every which way, like possessed antennae, trying SO hard to find a signal, she hopes will give us the right communication, that will get her message across. She tries SO hard to please us.
Apparently as a breed, Cairn Terriers are known for their great desire to please, and ability to read "their people's" body language.
She and I have conversations when its just the two of us in the quiet house. I tell her that she doesn't have to try so hard..., its ok to be more of herself,, we will love her no matter what.
I say "conversations", but I do all the talking, she just looks at me and listens, occasionally puts her paw gently on my leg, as if to say "its alright Mom, you don't have to try so hard, I love you no matter what."