Apart from Dullahans, any living being would die if their head were turned the other way around. However, the undead could cheat this manner of death.
This is what happened with the undead bear. It remained standing with a dislocated head swaying from left to right. The reanimated corpse refused to stay dead.
The lower jaw was severed after the head was forced to twist because the tendrils still impaled it. It remained attached to the tendrils like a trophy.
Zero could feel the jaw tremble as if it sought to reattach itself to the undead bear. Zero moved the tendrils from left to right and released the hold at the end of the swing. The lower jaw was thrown a meter or two away. Far enough for the undead bear to remain with a missing lower jaw.
One of the Cefeyes noticed a strange object on the ground. It grabbed this peculiar object, and it was too hot to hold.