The amount of dirt on Finney's face changes between shots while he digs at the basement floor.
The receiver on the black phone has different levels of tape damage in alternating camera angles.
Gwen's bicycle switches between having reflectors on the spokes and having none during her ride.
The Grabber's hair length appears slightly different between night scenes filmed in the same location.
In a background street shot, a car model newer than the film's 1970s setting is visible.
In one basement shot, a faint camera shadow briefly crosses the wall behind Finney.