When the two children escape through through the small hole, the boy goes in with one leg first, though on the other side he appears head first.
In the beheading scene, long shots of the severed head show the mouth closed, closeup shots show the mouth agape.
When Frankenstein's daughter looks at Nicholas (Joe Dallesandro) and then her brother, the liver of Frankenstein is seen behind her in the background. The final shot shows Frankenstein's liver in front of the daughter, meaning that the liver should be in front of her in the previous shot. Also, the liver and spear is slightly lowered in the final shot in comparison to the previous shot.
When Frankenstein "shocks" life into his creatures, him and Otto are touching the bodies with bare hands, yet they do not seem to be receiving any of the electricity.
Frankenstein created his zombies out of selected pieces of various people, and wanted to breed them to get offspring. However, regardless of the body parts he selected for each zombie, the offspring would only be a product of the reproductive organs, so choosing good brains/legs/arms etc would have made no difference at all.