Compared to the previous classes, the number of zombie slaves is very small, maybe not even one in ten thousand. It's not because the conditions for becoming a zombie slave are so harsh, or very few people are willing to become one.
On the contrary, most are willing to become zombie slaves, but such beings are just icing on the cake for zombies and aren't needed in large numbers. A few zombie slaves suffice to facilitate the management work of high-level zombies.
In other words, there's simply no condition to become a zombie slave!
