Revealing mistake: In the scene where Herbert and Dan re-animate the dead corpse, watch closely when Herbert rams the little buzz saw into the corpse's chest. At the bottom of the screen, you can see where the fake chest ends.
Continuity mistake: The glass window in the door to Dr. Hill's office is broken so that the main character and his girlfriend can enter. Later when Dr. Hill and his severed head return, the glass is perfectly fine.
Visible crew/equipment: In the scene where doctor Hill's body is walking about on its own in the lab, it is more than obvious that there is a crew member stood behind it, pushing it forward.