Other mistake: When Trash first comes back to life as a zombie there is a shot of rain falling and smoke swirling. The shot plays forward, then reverses for a second or two before playing forward again. The rain falls up and the smoke reverses direction.
Other mistake: When the zombies are climbing out of their graves, one is seen as a skull that rises, opens its eyes and mouth. If you look closely in its mouth you can see some kind of wire or control used to move the puppet. It is more clearly seen when the footage is reused at the end and the shot freezes for the closing credits on the same shot of the skull.
Revealing mistake: As zombie Freddy breaks down the door of the chapel, where he has been locked in, he rolls over a bench which is barricading the door. As he lays flat on the ground, about to get up, his shirt lifts up and you can see that not all of his stomach has been painted with "zombie skin color". (01:10:00)
Continuity mistake: Ernie is working on a cadaver when Burt arrives. After they cremate the body parts Burt brought over, there is one more shot where the feet of the cadaver can be seen under the blue sheet on the table. The next time we see the table, it is empty. It is never seen or referred to again.
Factual error: One zombie, who's rotted away all his organs, has two eyeballs looking good as new. Even if eyeballs didn't rot, they would fall out with nothing to hold them in. Just like the half of a woman zombie that talks with a soft sultry voice but with rotting or missing vocal cords.
Plot hole: After Frank and Freddie accidentally release the trioxin gas, there are several shots of the gas entering a return air vent and traveling through the heating, ventilation and air conditioning system belonging to the warehouse. Finally the gas exits into the freezer directly on to a hanging cadaver. This room was previously confirmed as a freezer and would have had its own self contained refrigeration system with its own ventilation system. Typical freezer doors also seal as they close. The cadaver would have never come into contact with the trioxin gas and would have never reanimated.