Well, it depends on they type of "zombie".
First you have your generic "Zeds". Mindless rotting bodies that have risen from the dead. Slow, shambling, silly, skulkers looking to suck snacks from said someone's with souls. ((thats alot of S's)) Basically, theyre dead. No soul. The soul left the body when they died. ((Old Horror movie zombies, or Possibly Dead Rising games. Not sure it kills and then animates corpses or infects, but i believe animates, thus being "Zeds".))
Then you have your "Infected". Fast with fleet feet moving in flurries causing fear! These "Zombies" are technically live. They have more brain function then a "Zed", thus allowing them to do more things. Running, jumping, fast crawling and partial climbing. They have souls, because they never really died. Basically mind control. ((L4D, or newer RE games.))
And last but not least of the major categories, "Magic Zombies". Im tired of rhyming so im just gonna say it straight forward. These are the LEAST LIKELY form of zombie, because magic is even more unlikely then Zombies. They are soulless, but bound to the body by a soul. Think of it like this. You sleep on a spring bed. You are not sleeping on springs, but on a padding, held to the springs. Just as the zombie is soulless, but bound by one. When you kill the zombie, you remove the binding of the soul, and thus, set the soul free. ((Diablo or Dark Souls))
And theres my beliefs on zombies and the different main breeds.