What an Ethernet splitter looks like
Partly because I couldn't easily turn up any good pictures of them on the Internet, here's a picture of an Ethernet splitter in its natural habitat:
(Full sized version here.)
The grey thing with the scratches in the background is the side of my office bookcase. Since this is a university, it is a dun metal one, hence the shade. (It may technically be some species of green. At a certain level of dull colouration, it becomes hard to tell.)
You will note that wisely, we have our data drops numbered and labeled. Given the chaos to be found in our wiring area, this is a really good idea. We even have maps with them all noted down, which is glorious and kind of miraculous.
(Carefully cropped out of this picture is the pair of very surplus thicknet Ethernet cables that dangle down from the ceiling just to the right of the junction box. I suppose I should go push them entirely behind the bookcase.)