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).
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.
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).
Bob Clark and his associates shot this film back-to-back with the horror film Children Shouldn't Play with Dead Things (1972). Both films were shot on location in Florida with much of the same cast and crew in both of them. Clark, Alan Ormsby, Jeff Gillen and other crew members would later reunite in 1974 to create the Canadian-made horror film Deranged (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.