In the bathroom, a lost boy had found someone to fight with:
This is a fairly common jumping spider, Trite auricoma. It doesn’t seem to have a common name, so you’d have to wonder how common it really is, but there are plenty of them around here.
It had wandered onto the mirror, and now refused to take notice of anything except its “opponent”. It started doing the same as I’ve seen them do when facing each other down for real: place its front pair of legs as wide as possible, and vibrate them slightly.
Eventually it did take some notice of the large flashing object getting in its face:
At this point I would have expected it to jump onto the camera but it turned and went back to its business with the other spider. And there it remained.
I should really have rescued it and taken it outside; but when this finally occurred to me (after I had taken all the photos and gone) it had disappeared.
Hopefully it will turn up again tomorrow.