Just like the phone cord ran up the wall (which–BTW–the phone works in its new home!), there was a mysterious cord running up the wall to nowhere in the dressing room.
It went up one side, around the ceiling, and down the other side–both ends of which were cut!
This is the other box I referenced in my first house project.
(I’m still not sure how to remove that box, as there was no obvious way for me to open it.)
Just like the phone cord, I cut the paint around the cord with a knife, and then pulled out the staples with pliers. I guess I didn’t get cut the paint well enough (plus there was more paint on this cord than the phone cord) which resulted in more damage to the ceiling and wall than expected.
Nothing that can’t be easily fixed before I paint!