After one woman gets her foot caught in a bear-trap, in one shot the man she was running with is kneeling down, trying to open the trap, but in the next shot he is standing up, and then he once again kneels down and then begins to try and open it.
Janet's hairstyle changes continuously throughout the film, even between the shots in some scenes.
When Michael is shown dead at the hands of Leslie, one of his arms has been removed and that arm is shown being consumed by Leslie. When Michael returns as a zombie in the film's final act, Michael has both arms intact.
After Evelyn has "killed" the zombie in the bathroom that is eating her son, she leaves the zombie body leaning on the bathtub, its mouth and eyes wide open. When after Evelyn has told the others about it, when one examines the bodies again later, the zombie's mouth is completely shut.
Michael says a rag "smells of death". The rag is thrown to the floor, but then disappears between shots.
While there really was a 14th century Italian Franciscan monk who went under the alias "Ragno Nero" (Black Spider) and made some eerily accurate predictions about future events, there is absolutely no record of him ever writing down a prophecy that claimed "the earth shall tremble....graves shall open....they shall come among the living as messengers of death and there shall be the nights of terror....''
Evelyn seemingly dies when Michael bites her. You cannot die from someone biting your nipple off, except from bleeding out, that is.
The faces of the actors playing zombies are clearly visible (though camouflaged with black paint) through the eye and mouth holes of their skull-like masks.
Obvious fake hand in close up of hand nailed to the window.
Obvious fire suit on the first zombie set on flame.
When people hide in passageway, film is clearly damaged on the lower side of the screen.
Michael moving his eyes while dead.
Right at the end of the film, when the two survivors are trapped in the workshop, the "Prophecy of the Black Spider" appears on the screen, for us to read. However in this prophecy, the word "nights" is wrongly spelled "nigths" and "prophecy" is spelled "profecy."
During the opening credits, several cars are seen driving along a winding two-lane road through the countryside. Several shots are POV from the passenger seat of one of the cars, with the steering wheel shown clearly on the left-hand side of the car, normal for left-hand drive. Yet the cars are all driving on the left ("wrong") side of the road, as though they are in the UK. When the cars pull up to the villa, we can clearly see an Italian number plate on the white Mercedes, so we know the scene is set in Italy (if the amphitheater ruins in the prologue weren't clue enough).
When creepy little Michael comes back to life, not only is his torn off arm back on, but when his mother offers him her breast to let him feed, when he bites her nipple off, gauze can be seen, clearly showing the less than special effect.
When the maid, whose hand is pinned to the shutter by a knife (why she doesn't pull it out is another silly idea), and the zombies cut her head off with a scythe, blood should come erupting out of the neck wound. Instead, her head rolls off the zombies grab it and nearly 30 seconds later, blood begins pouring out.
As Kathleen (the maid) is searching the house for zombies with a candle, and approaches the open window, the sound of her footsteps don't match her feet.
When Nicholas is talking to the professor, mouth movement and audio are not synchronized.
Shadow of camera on a zombie as it approaches the mansion, and nears the camera.
In the second shot of walking away from monastery a person can be seen moving at the left side of the screen.
Despite that some of the film's characters end up torn completely to pieces by the zombies, they still manage to come back to life without any explanation as to how their limbs were reattached.
At one point, a character rightfully declares that shooting the zombies in the head is the only way to kill them, although how he came upon this information is not explained. He shoots and kills a few zombies with a shotgun, then says they only have two shells left. When the zombies break into the mansion, the shotgun and tactic are both quickly forgotten.
At the end of the movie Mark is just bashing the zombie, but by then he knows that the only way to kill them is to destroy the head.
Why didn't they use the cars to run away.
When the survivors in the mansion are surrounded on all sides by tool-using, flesh-eating zombies, one character suggests that the zombies might just want something in the house instead of them. His solution to their predicament is to open the doors and let them in. Not that it matters, as the zombies know how to use a battering ram which they soon force the front door open. Plus, the theory of the zombies wanting something beside eating human flesh is never further explained.
At one point both groups of survivors gather in a long camera shot in front of the castle with three zombies visible. A woman is heard asking "where do we go now?" and the closest in frame zombie clearly raises his left hand and excitedly points in the direction and they all run that way.