My dog Sam goes absolutely ballistic when I return home from being out. For about 3 minutes he just goes wild jumping and licking and barking. Funny thing is if my girlfriend is asleep when I get home he does his entire ballistic routine in absolute silence so not to wake her up. He has been this was since a pup. I see this as a form of logic or could it be a holdover from some primitive advanatge to not waking the others in the pac. I know pointing dogs will freeze in their tracks if they see another dog on point, which is also a response to another dogs behaviour, could this be the same thing?
Mine does the same thing, even though there’s no one to wake up.
Area Man Greeted Enthusiastically by Pet Chihuahua
Anyone else read this thread to the tune of “My Sharona”? 
Well NOW I am, thanks to you. 
My first thought is nothing to do with primitive reasons or instinct, but because I am guessing you and your gf react differently to the dog: In her absense, [del]My Sharona[/del] your chihuahua doesn’t, somehow, get reinforced for making noise.
I came in to post that.
“M-m-m-my chihuahua…”
My my my my my WOOOO!
I was thinking up lyrics when I read your post:
Ooh my little shitty one, shitty one.
When you gonna hold it inside, Chihuahua?
Ooh you make my carpet dun, my carpet dun.
The smell is something I can’t abide, Chihuahua
Never gonna stop, shit it up.
Such a dirty mutt. Always shit it right at the sight
of another butt. My my my i yi woo. M M M My Chihuahua.
Darn you…I only opened this to post “Worst Clash song EVER!”
Except it was The Knack.
See, this is why I should have looked at Cat Whisperer’s post, muttered a choice curse and hit “back”… sigh
I see I’m not the only one who thought that.
“My Chihuahua!”