Continuity mistake: Marion isn't wearing any clothes as they enter the convenience store. However, as they are standing in the doorway you can see he is wearing boxers.
Continuity mistake: When the first zombie attack at Marion's house occurs, he throws his guns in the air, takes off hypocrite copper's shotgun and shoots a zombie. He then drops the shotgun and grabs his handguns. From the aerial shot the shotgun has disappeared. THEN the copper picks it up off the floor a few minutes later.