Werewolf Eddie needed to press the Play and Record button at the same time to record Terry's attack. But only the Play button was pressed down.
When Chris arrives at the colony in his Mazda, you hear the tires squeal, but his car is on the grass, not the cement.
In the gun fight scene with Slim Pickens, he first pumps the action on his rifle and fires a shot. When the camera cuts back to him he fires and reloads a bolt action rifle.
When Marsha makes the scratches on Bill's back, his back smooth and hair free. Yet the shot before showing them turning into werewolves, they were both covered with hair.
When Eddie is transforming into a wolf in front of Karen, his left hand turns gray and grows hair down to the knuckles. Then in the shot of his arm muscles expanding, his left hand has a normal skin color and hair only down to his wrist.
Slim Pickens is shot twice with the shots coming almost on top of each other in quick succession. However, he is shot with a manual bolt-action rifle making that impossible.
When Terry chops off a werewolf's arm (later revealed to have been T.C.), she is seen to chop it off about midway, just below the elbow. However, in the barn scene when he shows Karen what Terry did to him, he is shown to have his entire forearm, and is only missing his hand. That's because he was in the process of regenerating his arm.
The librarian even said "plus they regenerate" two days later they'd be good as new.
Many retail establishments in the movie have the names of outdated credit cards. MasterCharge is seen, but became MasterCard in 1979. BankAmeriCard is seen in several scenes, but became Visa in 1976. Strangely, the occult bookstore has signs for both BankAmeriCard AND Visa.
When Eddie has Karen White in the porno booth, he says, "None of them do. They're not real, the people here. They're dead. They could never be like me," but his mouth is almost always closed the whole time.
When Terry is in Dr. Waggner's office talking to Chris on the phone, there is an over-the-shoulder shot of Chris. Just before it cuts back to Terry in the office, a crew-member's shadow is visible moving toward Chris.