The Zombie Leveling System (ZLS for the sake of this article) is an ingenius method of rating zombies and their abilities. To the masterful eye of a zombie conisseur, any zombie can be instantly rated. The further a zombie has decayed, the higher it's level is. However, the decay level of a zombie eventually reaches a peak, in which its abilities are taken into account. The ZLS has taken into account several zombie abilties. Low level zombies merely have the ability to eat you and stumble around, should you be dumb enough to run into them. However, as zombies get higher in level, they become more agile, and gain abilities like spontaneous combustion, spikes, and wings. A level 50 zombie, is the most feared. Despite how rotten his flesh is his decayed brain can merely think about you, and you will die.
The rotten flesh zombie on fire, is about a level 20 on the Zombie Leveling System.