[nagdu] barking in harness?

[Daryl Marie]

Hey!
Just had a funny thing happen today. A group of us went out for lunch, then when we came back, Jenny just let out a couple of short barks (bark, pause, bark, pause, bark) at something or someone on the other side of the glass door leading to the office downstairs in our building. She was able to be redirected easily, so we went upstairs, took a 5-10-minute break, and went back downstairs (I thought she was barking at Gizmo, who I wrote about previously).  I figured, hey, training opportunity!
Well, we got downstairs, and again, she barked once at something on the other side of the door. I didn't hear anything or anyone, so I had her lie down by the second door (the one that leads upstairs), and I opened the door to the office downstairs, and there was nothing or no one there.
She has never done this before (except once at Gizmo), but people at work seem to think there's another dog down there.
Any pointers, advice?

Daryl