Polar Bear skulls and making them into headgear,
or taxydermy after deicide - designing Harrek's headgear.
After his return from his stint as Lunar dart warrior, having achieved the ultimate success in that game, Harrek slew the ancestral Polar Bear God Rathor, skinned him, and bound him to his skin.
The upper head still works like that of a life bear and sits atop Harrek's face.
This excellent picture of a polar bear skull:http://www.marinebio.net/marinescience/04benthon/arcimg/pb4219.jpg
can be found on this webpage on polar bearshttp://www.marinebio.net/marinescience/04benthon/arcplrbr.htm
This shows that keeping the lower jaw intact would make it rather impossible to fit a human skull under the upper part of the bear skull.
If you remove the lower part, you get something like a bone-made baseball cap with badass fangs on the front. Add a lot of fur on the outside and some as padding on the inside, and you have the makings of a believable helmet.
Harrek would want to retain the lower fangs, too, but not the entire lower jawbone - not enough space for his thick Rathori head to keep his moustache visible otherwise.
He'd probably keep the bit with the incisors and the canines, which would dangle below his chin like a necklace. The bits with the lateral teeth might remain, too, but not necessarily connected to the bit with the incisors and definitela not with the hinges.
I sort of dout that Harrek kept all the fur of his ancestral god. A polar bear standing upright is at least half again as high as a tall human, and the ancestral bear god would probably tower over an ordinary polar bear.
He performed the skinning invading an annual rite of his people, probably dismembering the bear god with a few mighty strokes while binding its spirit into the fur of the head. What Harrk wears is the upper part of the fur covering Rathor's back and forelegs, but none of the belly or hindquarter.
The front of the forepaws with the claws remained. The upper head remained. The lower head including the jaw hinges was most likely shattered in the process. Harrek might have put some extra fur into the skull cavity as padding before putting it onto his own head, or he might have relied on his own mane to provide for that.
Harrek being Harrek, he probably didn't make a hasty escape but shambled away like a bear leaving the remnants of a carcass to the scavengers. The Rathori audience will have been stunned at the sacrilege, but now some braves would rush forward to attack Harrek, only to be swiped aside with the paws and power of their ancestral god. Roaring his annoyance and ignoring the feeble Rathori attempts to pierce the skin with their longbows, his menacing presence would have quelled the fighting spirit of everyone facing Harrek's blood-covered snarl. Giving him way to disappear into the night.
Harrek still wears the fur as it was when he took it. The muscles of the upper head still appear to work, as do those of the claws.
Other parts of the fur hang loosely, like any product of taxydermy. I think that this applies to the lower jaw most of the time.
The bear god might still be able to manifest an intact body replacing all the missing parts by magic, but normally it makes do with the physical remains – the muscles mentioned above. It still retains its breath (probably along with the predatory tang), without any need for lungs. Its power flows through Harrek's body. His description as the slayer of Ignifer would be even more true after taking in the bear god.
I suppose that binding the spirit or magic of a slain prey into a trophy is a fairly standard magic for heroic hunters – not necessarily a Rathori custom, though, unless this is how hunting charms are made. Applying it to the ancestral forefather of all is on a level to make Eurmal wish he had tried it.