When Carol arrives at the doctor's house, the garage door is up. Minutes later, when Alex leaves in the hat and trenchcoat through the front door, the garage door is closed.
Before the gas station attendant is about to grab Dr Alex Marsh's arm, the back of the attendant's hand is already darkened black before making contact.
When Dr Alex Marsh is talking to elderly Dr Ramsey over the phone and later in person, Alex sequentially asks where Carol is three times with Dr Ramsey giving the same answer that she and Tom are going or went out to dinner.
Jack Donner was erroneously listed as Jack Doner in the opening credits.
When the monster turns the light on in the beachfront house, instead of turning the handle on the lamp, it turns on by his touch. Those lamps turned on and off by turning the handle clockwise.
When the monster enters the cab, he taps the driver's shoulder. This should have killed the driver.