SUMMARY: They're barking at--what?
This evening, while cleaning the shower in my bedroom, I hit one wall with the scrub brush. Tika apparently felt that this was indicative of someone trying to break into the house, sprang from the bed, and leaped into the hallway in full ferocious Tika barking mode and wouldn't shut up no matter what I yelled (but I'll admit that I didn't try "speak"-- which works SO much better with her than "quiet").
Boost, apparently startled by the noise and/or Tika's reaction, was in full Repelling Boarders outcry at SOMETHING IN THE CORNER OF MY ROOM when I emerged from the bathroom. I was pretty sure that nothing and no one dangerous had snuck into my bedroom in the two minutes I'd been in the bathroom, but seeing that behavior in your dog none-the-less makes the hair stand up on the back of your neck.
Until you realize that what she was protecting you against was the blue merle border collie on the other side of the...mirror. Same mirror that's been in that room, in the same place, for the last 2 years and 10 months since she arrived. And she can't spend more than, oh, 10 or 12 hours a day in that room.
I'm so glad that I have such brave dogs identifying such horrific threats in my home. I feel so safe!