Zone One

In the first 81 pages of Zone One I found some things very interesting and  things confusing.  Right now I am finding the book a little hard to understand, I find myself thinking a lot trying to figure out what is going on.  I am confused on weather or not Mark is dead or alive.  He keeps talking about know the zombies or a least seeing people he knows in the faces of them and I am confused by that. Is it possiable that he knows all of the undead that is walking around with him? Therefore, I'm not sure yet on if I like the book I'm looking forward to reading more and see where it takes me.