During a scuffle between George and Gil at Trudy's house, George pulls out a Colt Model 1903 handgun and forces Gil outside. But when the scene resumes outside, the gun is now a Luger.
Towards the end of the film in two shots separated by a shot of the monster wrestling with a policeman, two police cars arrive at the gas holder from different directions - they both have the same license plate number (PBU 839).
When the doctor is talking about how humans develop in the womb, he places a picture of a cro-magnon man on top of another book showing pictures of "intermediate classes" of animals. When he removes the picture, however, the book is showing pictures of the developing stages of a human.
When Gil fight the cop on the top of the storage tank he has stains on both the front and the back of his pants. In the next scene as he runs up the stairs the stain on the front is not there but when he turns to confront the cop it has reappeared.
The barrel of the police officer's rubber prop gun visibly bends back and forth as he is chasing the Sun Demon on top of the gas tank.
The close shots of Gil and the policeman fighting on the top of the gas tank show another flight of ascending stairs to their right, yet when seen from the ground, they are clearly at the very top.
Two minutes into the movie Dr. Gilbert McKenna is described as both iconic and obscure, each being the polar opposite of the other.
When Dr. Buckell pulls up in his car to buy a newspaper from the paperboy, the reflection in the car's passenger door reveals the newspaper is being handed to him through the open window by a female production assistant wearing a white blouse and black skirt.