Danny DeVito won his role of Fly Speck because he and Kirk Douglas' son, Michael Douglas, were best friends and had been roommates in college.
Françoise Pascal was first offered the part of Lucy-Ann. But she turned down the role so she could do The Iron Rose (1973).
Actor Neville Brand played dual roles in the movie portraying the two twin brother characters of ''Mudhook'' and ''Brimstone''.
The film was re-rated 'G' on appeal after originally receiving a 'PG' rating from the MPAA (Motion Picture Association of America). This occurred after filmmaker Kirk Douglas complained to the Ratings Board as reported in the 22nd March 1973 issue of show-business trade-paper 'Daily Variety'.