Richard Backus was cast as Andy in the film because he was able to create a silent stare of intense hatred for the casting agent. Backus' creepy facial expression came into play frequently in it.
In the film's final scene in Brooksville Cemetery, a tombstone with the name "Daily" is seen over Andy's shoulder. The same tombstone appears in another one of Bob Clark's horror films, Children Shouldn't Play with Dead Things (1972).
Portions of Carl Zittrer's music score for this film were later reused and expanded upon for another one of Bob Clark's horror films, Black Christmas (1974).
Alan Ormsby: the writer of the film's screenplay, who played the man who tells Charlie that Doc Allman has been killed. Ormsby was married to Anya Ormsby (who played Cathy Brooks in the film) at the time. Their young son made a cameo appearance in it as the crying boy in the scene where Andy kills the dog.