The film was entirely financed thanks to Marlon Brando's participation. Marquand and Brando knew each other for a long time and were good friends. Brando agreed to do the film as a favor to his friend. Marquand had helped with negotiations with French Premier George Pompidou in his purchase of the Tahitian island of Tetiaroa. He didn't particularly like the script but he had fun shooting his sequence. Then other stars agreed to play a part in the movie and it was even easier to convince the producers.
In one sequence, Charles Aznavour (as the hunchback) escapes the police by crawling on the mansion ceiling and jumping down through a window made of water. This is a visual reference to surrealist Jean Cocteau's The Blood of a Poet (1932) where the character jumps into a mirror made of water after crawling over a hallway of doors. (The effect was achieved by constructing the "wall" and "ceiling" on the studio floor and shooting the scene from above.) Even the sound effect at that moment, a shouted "No!", is in both films.
James Coburn's character is called 'Dr Krankheit': 'Krankheit' means 'illness' in German. 'Dr Kronkheit' is also the name of a celebrated vaudeville routine, where a patient visits an inept doctor ('Kronkheit' is the Yiddish equivalent). This sketch was made famous by Joe Smith and Charles Dale, who can be seen performing it in Two Tickets to Broadway (1951); it was reprized in The Sunshine Boys (1975) by Walter Matthau and George Burns.