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.
Factual error: After trying to devise a plan to get rid of the "evidence", Burt runs up metal stairs and peeps out the window looking over in the direction of the cemetery and confirms Ernie Kaltenbrunner is still working. The lights in the funeral home were all off except for the embalming room where Ernie was working. As seen through the entire film the cemetery main gate seems to be the primary entrance onto the Resurrection Funeral Home property. In order to carry the evidence on a stretcher to the funeral home Frank, Freddie and Burt would have had to walk though the cemetery in order to get to the embalming room entrance and would have run into the punks and their party.
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.
Burt Wilson: What about the bones Ernie?
Ernie Kaltenbrunner: Bones are no problem. Hardest thing to burn is the heart.
Burt Wilson: A heart, why?
Ernie Kaltenbrunner: 'cause it's just one big tough muscle.
Burt Wilson: Yeah, but Ernie, I mean, c'mon, we don't want the heart sticking around.
Ernie Kaltenbrunner: Then I'll turn it up hotter for the heart.