What's that -- a head?
What I was actually doing in the archive is something I've found very fruitful: find a town with a big cathedral, look under "Sammlungen" (collections) for its "Dommuseum" (cathedral museum) or "Diozesanmuseum" (diocesan museum), go to the folder labeled "Kunstgewerbe" (applied arts) and look at everything under "Schmuck" (which roughly means "decoration" or "jewelry"). Some very interesting and unexpected things turn up.
Anyway, most of the prayer nuts you see illustrated in art books are the most intricate ones, with five or six scenes inside and with the outside intricately carved in a ribbed or interlace pattern. This one's a bit more modest. The outside is shaped into a woman's head, probably representing the Virgin Mary.
Inside are two carved scenes. I am fairly sure that the top scene in this photo, Christ carrying his cross, is inside the front of the head, and the bottom scene, the Crucifixion, is inside the back half. If you try to imagine how this prayer-nut is put together, you will realize that the top scene is actually placed into the front of the head upside-down, so that when the nut is opened like this, both scenes will be right side up.
The bottom of the closed nut is carved with an interlace design like the frame around the inside scenes.
Above the hook, it looks as though some kind of crest or coat of arms is carved within a rather eccentric-shaped German shield. It looks to me like what's on the shield is the top half of a rampant lion -- head and front paws, facing to the left as you look at it. This may be a mark of ownership. The sort of wealthy citizen or noble who would have bought such a prayer-nut was very conscious of family connections, and could certainly have ordered it "customized" in this way. Like many expensive accessories, a custom-made prayer nut like this was worn at least as much a sign of the owner's wealth, success, and good taste as it was for any religious reason.