Damage is also caused by other factors. Fingerprints leave behind oils and dirt. Film can be scratched and torn by projectors that have not been properly maintained or by improper threading of film in the projector. Projectors grip and pull film by the perforations (sprocket holes) along the edges; these perforations can easily be torn, often leading to extensive damage to the film. Depending on the extent of the damage, torn film and broken sprocket holes can usually be repaired.