How they work, what laws they follow and what kinds there are
The average fast walking zombies that roam in hoards. Mindless zombies that has a range of strengths but their sole strength being their numbers. They track by sound and smell. They are fast, speratic and unpredictable, but they always travel in groups. If there's one, more will be close behind. They move faster than the average person and if you're not careful they will easily outnumber you, trapping you within the horde and you will have no chance of escaping. They can be dispatched of easily with guns or loud noises, but that will only attract more of them, as well as attracting the attention of things far worse than these guys...
They look like the typical human, but slowly decaying skin and bones, golden eyes, and tend to shuffle about until they are alerted to your presence. Their senses of smell are equal to that of normal humans and can be lured away easier than the others.
Runners
They are the faster, scarier, and more deadly evolved forms of zombies. They're usually seen in a small group or by themselves, but more will come once they're alerted as they give off a scream whenever they're bothered with. Their sense of smell and hearing is far better than the average zombie and even better than the normal person's. They can be lured away with a fresh human kill or a sound in the distance, but you better watch out or even a single hitch of your breath can alert them to your presence. In that case, all you can do is run and pray to god that you're fast enough to outrun them.
Crawlers
Zombies that have lost the ability to walk resulting in them crawling among the ground. They are slow moving but are able to sneak up on anyone and are much harder to locate or identify as dead. They tend to be located hidden out of sight, out of mind or in the middle of hoards. they tend to be weak aside from their firm grip and strong bite. They track by sound and smell.
Trackers
Unlike the others, they are blind, therefore they rely heavily on their senses of smell and hearing. If they are deafened then they can easily be overpowered, but don't underestimate them as they rely on echolocation and can be a deadly force to be reckoned with in numbers. They are more often than not what alerts others to the presence of humans and can be easily taken out if you have a clear shot on them.
Banshees
They resemble shamblers but have their vocal cords entirely intact and are able to emit a high pitch scream that stun anyone within fifteen feet and draws in zombies within five miles. They also have acute hearing being able to hear the very breathing of its prey even among a bunch of moaning zombies. Aside from that they are the same as shamblers. They track by sound and smell.