In the anime, the zombie trolls are depicted as the reanimated bodies of the subject at the moment of its demise. Meaning that if the body is well preserved at the moment of the reanimation, the zombie could pass as living in the eyes of those who do not possess skills to recognize the undead.
Zombie Trolls are trolls that have been turned into an undead, losing all the abilities related to their biological functions, like regeneration; but at the same time gaining all the other general racial abilities of the undead.
Not knowing that Guu has become a Zombie Troll after it got killed by Ainz, Jugem has taken into consideration that he seems to lack the ability to regenerate. This could hint on the notion that Zombie Trolls like Guu are unable to retain their racial ability to regenerate like the other troll variants after turning into an undead.
- Ainz considered the thought of using Guu's corpse as a reference for making Zombie Trolls in the future.